Electrochemical capture of lewis acid gases

Abstract

To provide methods, apparatuses, and systems related to electrochemical capture of Lewis acid gases.SOLUTION: Methods, apparatuses, and systems related to electrochemical capture of Lewis acid gases from fluid mixtures are generally described. Certain embodiments are related to electrochemical methods involving selectively removing a first Lewis acid gas from a fluid mixture containing multiple types of Lewis acid gases (e.g., a first Lewis acid gas and a second Lewis acid gas). Certain embodiments are related to electrochemical systems comprising certain types of electro active species having certain redox states in which the species is capable of binding a first Lewis acid gas but for which binding with a second Lewis acid gas is thermodynamically and / or kinetically unfavorable. The methods, apparatuses, and systems described herein may be useful in carbon capture and pollution mitigation applications.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Related Applications This application is filed under 35 U.S.C. § 119(e) with the same application number as the application filed on August 28, 2019, entitled "Electrochemically Mediated Acid Gas Removal and Concentration Method." No. 62 / 892,975, filed March 12, 2020, entitled "Electrochemical Capture of Lewis Acid Gases," and U.S. Provisional Application No. 62 / 892,975, filed March 12, 2020, entitled "Electrochemical Capture of Lewis Acid Gases." Priority is given to U.S. Provisional Application No. 62 / 988,851, entitled "Capture of Lewis Acid Gases." No. 6,119,233, filed on Dec. 1, 2007, and claims priority to U.S. Provisional Patent Application No. 2005 / 0100999, each of which is incorporated herein by reference in its entirety for all purposes.

[0002] Technical Field Methods, devices, and systems for the electrochemical capture of Lewis acid gases from fluid mixtures are generally described. [Background technology]

[0003] background Efforts have been made to remove or separate gases from fluid mixtures. For example, over the past two decades, efforts have been made to mitigate global temperature rise by curbing anthropogenic carbon dioxide (CO2) emissions. Several approaches have been explored to address the capture of carbon dioxide at various stages of its production, such as traditional thermal methods of capturing it after combustion in power plants or concentrating it from the atmosphere and then pressurizing it into geological formations for storage or conversion to commercially useful compounds. One alternative approach is the electrochemical capture of gases using electroactive species. However, difficulties can arise in removing or separating a particular gas (e.g., carbon dioxide) from a fluid mixture containing multiple different types of gases (e.g., multiple types of Lewis acid gases).

[0004] Improved apparatus, methods, and / or systems are desirable. Summary of the Invention [Means for solving the problem]

[0005] overview Methods, devices, and systems related to the electrochemical capture of Lewis acid gases from fluid mixtures are generally described. Certain embodiments relate to electrochemical methods that include selectively removing a first Lewis acid gas from a fluid mixture containing multiple types of Lewis acid gases (e.g., a first Lewis acid gas and a second Lewis acid gas). Some embodiments involve methods that include selectively removing the Lewis acid gas by combining the first Lewis acid gas and the second Lewis acid gas with one or more reduced electroactive species, and then selectively releasing the second Lewis acid gas from the resulting composite while releasing relatively little or no first Lewis acid gas from the composite. Certain embodiments relate to electrochemical systems that include certain types of electroactive species that can combine with a first Lewis acid gas but have a particular redox state in which combining with a second Lewis acid gas is thermodynamically and / or kinetically unfavorable. The methods, devices, and systems described herein may be useful in carbon capture and pollution abatement applications. The subject matter of the present invention includes, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0006] In one aspect, a method is described. In some embodiments, the method includes applying a potential difference across an electrochemical cell, exposing a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas to the electrochemical cell, and removing an amount of the first Lewis acid gas from the fluid mixture during and / or after the application of the potential difference, wherein the method includes removing from the fluid mixture essentially none, or 10% or less by mole percent, of the second Lewis acid gas present in the fluid mixture.

[0007] In some embodiments, the method includes exposing a fluid mixture including a first Lewis acid gas and a second Lewis acid gas to one or more electroactive species in a reduced state; combining a quantity of the first Lewis acid gas with a first portion of the one or more electroactive species in a reduced state to form a first Lewis acid gas-electroactive species composite; and combining a quantity of a second Lewis acid gas with a second portion of the one or more electroactive species in a reduced state to form a second Lewis acid gas-electroactive species composite. forming an activated species composite; and oxidizing at least a portion of the second Lewis acid gas-electroactive species composite such that an amount of the second Lewis acid gas is released from the second Lewis acid gas-electroactive species composite while essentially no first Lewis acid gas is released from the first Lewis acid gas-electroactive species composite, or an amount of the first Lewis acid gas released from the first Lewis acid gas-electroactive species composite that is 10% or less by mole percent of the amount of the first Lewis acid gas-electroactive species composite.

[0008] In another aspect, an electrochemical device is described. In some embodiments, the electrochemical device includes a negative electrode in electronic communication with an electroactive species, and a fluid mixing The method includes a chamber configured to receive an item in at least one electrically conductive medium, wherein the electroactive species has an oxidized state and at least one reduced state in which the electroactive species can combine with a first Lewis acid gas, but reaction with a second Lewis acid gas comprising one or more species selected from carbon dioxide, nitric oxide, RB, or RS (each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl) is thermodynamically and / or kinetically unfavorable at at least one temperature. In some embodiments, the electroactive species has at least one reduced state in which the electroactive species can combine with a first Lewis acid gas, but reaction with a second Lewis acid gas comprising one or more species selected from carbon dioxide, nitric oxide, borane, or hydrogen sulfide (HS) is thermodynamically and / or kinetically unfavorable at at least one temperature of 223 K or greater and 573 K or less.

[0009] Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification will control.

[0010] Non-limiting embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale. Each identical or nearly identical component shown in the drawings is typically represented by a single numeral. For clarity, not every component is labeled in every drawing, nor is every component in every embodiment of the present invention shown, unless illustration is necessary for those skilled in the art to understand the invention.

[0011] The figure is described in accordance with the following text. [Brief explanation of the drawings]

[0012] [Figure 1A] 1A-1B are schematic diagrams of an exemplary process for removing a first Lewis acid gas from a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas, according to one or more embodiments. [Figure 1B] 1A-1B are schematic diagrams of an exemplary process for removing a first Lewis acid gas from a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas, according to one or more embodiments. [Figure 2] FIG. 2 is a schematic cross-sectional view of an electrochemical device including a chamber constructed to receive a fluid mixture and a negative electrode, according to one or more embodiments. [Figure 3] FIG. 3 is a schematic diagram of an exemplary process for removing a first Lewis acid gas from a fluid mixture including a first Lewis acid gas and a second Lewis acid gas, in accordance with one or more embodiments. [Figure 4] FIG. 4 is a schematic cross-sectional view of a flow device including a first electrochemical cell and a second electrochemical cell according to one or more embodiments. [Figure 5] FIG. 5 shows a schematic side view of an exemplary electrochemical cell including a negative electrode, a positive electrode, and a separator according to one or more embodiments. [Figure 6] FIG. 6 shows a schematic exploded view of an exemplary electrochemical cell according to one or more embodiments. [Figure 7A] FIG. 7A shows a schematic diagram of an exemplary system for performing a gas separation process, according to one or more embodiments. [Figure 7B] FIG. 7B shows a schematic diagram of an exemplary system including a flow field for performing a gas separation process, according to one or more embodiments. [Figure 7C] 7C-7E show schematic side views of exemplary flow field channel patterns according to one or more embodiments. [Figure 7D]7C-7E show schematic side views of exemplary flow field channel patterns according to one or more embodiments. [Figure 7E] 7C-7E show schematic side views of exemplary flow field channel patterns according to one or more embodiments. [Figure 8A] FIG. 8A shows a schematic diagram of an exemplary system including multiple electrochemical cells for performing a gas separation process, according to one or more embodiments. [Figure 8B] FIG. 8B shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in parallel to perform a gas separation process, according to one or more embodiments. [Figure 8C] FIG. 8C shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in series to perform a gas separation process, according to one or more embodiments. [Figure 9] FIG. 9 shows a schematic diagram of an exemplary system including multiple electrochemical cells electrically connected in series to perform a gas separation process, and one or more electrically conductive materials between the electrochemical cells, according to one or more embodiments. [Figure 10A] Figure 10A shows the cyclic voltammetry of 1,4-naphthoquinone (p-NQ, alternatively labeled NQ) in dry N,N-dimethylformamide solution containing 0.1 M tetra-n-butylammonium hexafluorophosphate ([nBu4][PF6]) saturated with either N2, CO2, or SO2. [Figure 10B] FIG. 10B shows the cyclic voltammetry of 2,3-dicyano-1,4-naphthoquinone (DCNQ) in dry N,N-dimethylformamide solution containing 0.1 M [nBu4][PF6] saturated with either N2, CO2, or SO2. [Figure 11A] Figure 11A shows the thermogravimetric analysis (TGA) of DCNQ2-, NQ·-, and NQ2- under 1% SO2. [Figure 11B]Figure 11B shows the TGA analysis of DCNQ2-, NQ·-, and NQ2- in N2. [Figure 11C] FIG. 11C shows TGA measurements of SO2 uptake by NQ2- at different temperatures. [Figure 11D] FIG. 11D shows the TGA measurements of SO2 uptake and release by NQ2- at different temperatures. [Figure 11E] FIG. 11E shows TGA measurements of SO2 uptake by DCNQ2- at different temperatures. [Figure 11F] FIG. 11F shows TGA measurements of SO2 release by DCNQ2- at different temperatures. [Figure 12A] FIG. 12A shows TGA measurements of CO 2 capture using reduced DCNQ at 30° C. under 100% CO 2 . [Figure 12B] FIG. 12B shows TGA measurements showing that CO2 is released when the reactants are removed. [Figure 13A] 13A-13C show the calculated change in geometry of DCNQ upon reduction. [Figure 13B] 13A-13C show the calculated change in geometry of DCNQ upon reduction. [Figure 13C] 13A-13C show the calculated change in geometry of DCNQ upon reduction. [Figure 14A] FIG. 14A shows electrostatic potential (ESP) maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective neutral states. [Figure 14B] FIG. 14B shows ESP maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective semiquinone states. [Figure 14C] FIG. 14C shows ESP maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective dianionic states. [Figure 15A]15A-15D show the calculated geometry and ESP maps of CO2 and SO2, respectively. [Figure 15B] 15A-15D show the calculated geometry and ESP maps of CO2 and SO2, respectively. [Figure 15C] 15A-15D show the calculated geometry and ESP maps of CO2 and SO2, respectively. [Figure 15D] 15A-15D show the calculated geometry and ESP maps of CO2 and SO2, respectively. [Figure 16] FIG. 16 shows a schematic diagram of a gas separation experiment, according to one or more embodiments. [Figure 17A] 17A-17B show plots of the ratio of effluent gas concentration to influent gas concentration versus time for physisorption and chemisorption experiments according to one or more embodiments. [Figure 17B] 17A-17B show plots of the ratio of effluent gas concentration to influent gas concentration versus time for physisorption and chemisorption experiments according to one or more embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0013] Detailed Description Methods, devices, and systems related to the electrochemical capture of Lewis acid gases from fluid mixtures are generally described. Certain embodiments relate to electrochemical methods that include selectively removing a first Lewis acid gas (e.g., sulfur dioxide) from a fluid mixture containing multiple types of Lewis acid gases (e.g., a first Lewis acid gas and a second Lewis acid gas (e.g., carbon dioxide)). Some embodiments relate to methods that include selectively removing the Lewis acid gas by combining the first Lewis acid gas (e.g., sulfur dioxide) and the second Lewis acid gas (e.g., carbon dioxide) with one or more reduced electroactive species, and then selectively releasing the second Lewis acid gas from the resulting complex (e.g., by oxidation of the second Lewis acid gas-electroactive species complex), while releasing relatively little or none of the first Lewis acid gas from the complex. Certain embodiments relate to electrochemical systems that include certain types of electroactive species that can bind to a first Lewis acid gas but have a particular redox state in which binding with a second Lewis acid gas is thermodynamically and / or kinetically unfavorable. The methods, devices, and systems described herein can be useful in carbon capture and pollution abatement applications.

[0014] The removal and / or separation of Lewis acid gases in fluid mixtures is an important process in several applications, including industry and power generation. As an example, sulfur dioxide (SO2) emissions are traditionally reduced in industrial applications by flue gas desulfurization (FGD), which relies on large absorber contact towers (scrubbers) with a large footprint and balance of plant. Furthermore, there are many other applications where it may be desirable to remove Lewis acid gases, e.g., SO2, from flue gases or other industrial gas streams to avoid complications with downstream processes or for other reasons, such as pollution abatement. For example, the International Maritime Organization (IMO) has introduced a sulfur cap. cap), which came into effect in January 2020. Many ships are now operating under the traditional While ships are being retrofitted with scrubbers, small vessels cannot accommodate such chemical plants on board. Therefore, a compact and efficient Lewis acid gas capture system is needed. Electrochemically mediated gas capture can be one route for capturing Lewis acid gases (e.g., by electrochemically generating an active state of electroactive species capable of binding to a targeted gas). However, aggravating factors include the fact that many fluid mixtures (e.g., exhaust gas) contain multiple Lewis acid gas species, and it may be desirable to selectively remove a first Lewis acid gas while removing essentially none or relatively little of the other Lewis acid gases. As an example, combustion products often include carbon dioxide and sulfur-containing gases, such as SO2. It has been found in the context of the present disclosure that certain existing electroactive species in electrochemical systems can react with both the first and other Lewis acid gases, which can be problematic. For carbon capture systems designed to remove carbon dioxide from gas mixtures, the presence of sulfur dioxide can pose efficiency and capacity challenges because sulfur dioxide can compete with carbon dioxide for binding to the electroactive species. It has been discovered in the context of the present disclosure that certain methods and systems can be used to selectively bind certain Lewis acid gases over others (e.g., by judicious selection of electroactive species and / or operating conditions).

[0015] In one aspect, a method is described. Some embodiments include a method for partial or complete electrochemical removal and / or separation of Lewis acid gases in a fluid. Some embodiments include applying a potential difference across an electrochemical cell and exposing a fluid mixture including a first Lewis acid gas and a second Lewis acid gas to the electrochemical cell. FIGS. 1A-1B illustrate one such embodiment, in which a fluid mixture 101 including a first Lewis acid gas 102 and a second Lewis acid gas 104 is exposed to an electrochemical cell 100. The term "electrochemical cell" is intended to include devices that meet these criteria, even if the behavior of the cell can arguably be characterized as more pseudocapacitive than faradaic, and thus may alternatively be referred to as a type of capacitor.

[0016] By applying a potential difference across the electrochemical cell, during application of the potential difference and / or After application, a quantity of the first Lewis acid gas can be removed from the fluid mixture. For example, referring again to FIGS. 1A-1B, in the absence of a potential difference, electrochemical cell 100 can be in electronic communication with electroactive species in an oxidized state Ox that are not bound to the first Lewis acid gas (FIG. 1A). By applying a potential difference across electrochemical cell 100, according to some embodiments, the electroactive species can be converted to a reduced state R that reacts with (e.g., by binding to) the first Lewis acid gas 102 (FIG. 1B). While FIGS. 1A-1B show fluid mixture 101 exposed to electrochemical cell 100 with electroactive species in an oxidized state Ox, it should be understood that some embodiments include applying a potential difference across electrochemical cell 100 before exposing electrochemical cell 100 to fluid mixture 101, such that at least one electroactive species in a reduced state (e.g., R) is generated prior to exposure to fluid mixture 101.

[0017] In some embodiments, the method includes removing essentially no or relatively little, by mole percent, of the second Lewis acid gas present in the fluid mixture from the fluid mixture. For example, referring again to FIG. 1B , upon application of a potential difference across electrochemical cell 100, essentially no second Lewis acid gas 104 is removed from fluid mixture 101 (e.g., by reacting with electroactive species in the reduced state R produced by the application of the potential difference, in contrast to first Lewis acid gas 102). In some cases, essentially no or relatively little removal of the second Lewis acid gas from a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas can be beneficial when it is desired to produce a fluid mixture relatively free of the first Lewis acid gas. As a non-limiting example, a fluid mixture may include carbon dioxide (CO ) and sulfur dioxide (SO ), but it is desirable for the fluid mixture to contain only CO (e.g., for a downstream carbon capture process). Thus, in some embodiments, by applying a potential difference to an electrochemical cell and exposing a fluid mixture to the electrochemical cell, some (or all) of the SO may be removed, while essentially none or relatively little of the CO is removed. The reduced concentration of SO in the fluid mixture after performing such a method may increase the efficiency and / or capacity of downstream processes involving the fluid mixture.

[0018] Removing a quantity of a first Lewis acid while essentially none or relatively little of a second Lewis acid can be achieved according to any of the various techniques described herein (alone or in combination). For example, removing a quantity of a first Lewis acid while essentially none or relatively little of a second Lewis acid can include exposing a fluid mixture containing a first Lewis acid gas and a second Lewis acid gas to conditions configured such that the first Lewis acid gas binds to electroactive species while the second Lewis acid gas does not bind to the electroactive species (e.g., for thermodynamically unfavorable or kinetic reasons). In some embodiments, the conditions are configured such that both the first Lewis acid gas and the second Lewis acid gas are capable of binding to the electroactive species, but the first Lewis acid gas has a higher affinity for the electroactive species (as measured by the parallel binding constant) than the second Lewis acid gas under operating conditions. With some such configurations, the second Lewis acid gas (e.g., carbon dioxide) can reversibly bind to the electroactive species and the first Lewis acid gas can irreversibly bind to the electroactive species, such that the first Lewis acid gas outcompetes and / or displaces the second Lewis acid gas. The end result of such reactivity is that some amount of the first Lewis acid gas is removed from the fluid mixture, but relatively little or none of the first Lewis acid gas is removed, despite the formation of a first Lewis acid gas-electroactive species complex during at least a portion of the overall process. In yet another version, the first Lewis acid gas can be removed by combining the first Lewis acid gas and a second Lewis acid gas (e.g., carbon dioxide) with one or more reduced electroactive species, and then selectively releasing the second Lewis acid gas from the complex (e.g., by oxidation or temperature change of the second Lewis acid gas-electroactive species complex) while releasing relatively little or none of the first Lewis acid gas from the complex.

[0019] In some embodiments, the method comprises removing an amount of a first Lewis acid from a fluid mixture and removing from the fluid mixture, by mole percent, 10% or less, 5% or less, 1% or less, 0.5% or less, 0.1% or less, 0.05% or less, 0.01% or less, 0.001% or less, and / or no more than 0.0001%, no more than 0.00001% or less of a second Lewis acid gas present in the fluid mixture. In some embodiments, the method comprises removing from the fluid mixture, by volume percent, 10% or less, 5% or less, 1% or less, 0.5% or less, 0.1% or less, and / or no more than 0.05%, no more than 0.01%, no more than 0.001%, and / or no more than 0.0001%, no more than 0.00001% or less of a second Lewis acid gas present in the fluid mixture. In some embodiments, essentially no second Lewis acid gas is removed during the performance of the method (e.g., none or only a small amount is removed for purposes of the fluid mixture, such as carbon capture or production of purified gas).

[0020] The potential difference applied across the electrochemical cell can be performed in a charging mode. In the charging mode, a redox half-reaction occurs at the negative electrode, where the negative electrode electroactive species is reduced. The potential difference applied across the electrochemical cell during the charging mode can have a specific voltage. The potential difference applied across the electrochemical cell can depend, for example, on the standard reduction potential for the generation of at least one reduced state electroactive species and, if present, the standard reduction potential for the interconversion between the reduced state of a second electroactive species and the oxidized state of a second electroactive species. In some embodiments, the potential difference is at least 0 V, at least 0.1 V, at least 0.2 V, at least 0.5 V, at least 0.8 V, at least 1.0 V, at least 1.5 V, or higher. In some embodiments, the potential difference is 2.0 V or less, 1.5 V or less, 1.0 V or less, 0.5 V or less, or less. Combinations of these voltages are also possible. For example, in some embodiments, the potential difference applied across the electrochemical cell is at least 0.5 V and is 2.0 V or less. Other values ​​are possible.

[0021] The potential difference applied across the electrochemical cell may be performed in a discharge mode, in which a redox half reaction occurs at the negative electrode, in which electroactive species at the negative electrode are oxidized. The potential difference across the electrochemical cell during the discharge mode can have a particular voltage. For example, in some embodiments, the potential difference can be less than 0 V, -0.5 V or less, -1.0 V or less, or -1.5 V or less. In some embodiments, the potential difference can be at least -2.0 V, at least -1.5 V, at least -1.0 V, or at least -0.5 V. Combinations of these voltages, such as at least -2.0 V and -0.5 V or less, are also possible. Other values ​​are also possible.

[0022] The fluid mixture exposed to the electrochemical cell can be any of a variety of forms and compositions. In some embodiments, the fluid mixture is a gas mixture. For example, fluid mixture 101 of FIGS. 1A-1B is a gas mixture containing first Lewis acid gas 102 and second Lewis acid gas 104 upon exposure to electrochemical cell 100, according to some embodiments. In some embodiments, the fluid mixture is a liquid mixture. For example, fluid mixture 101 of FIGS. 1A-1B is a liquid mixture containing a liquid (e.g., a solvent) in which first Lewis acid gas 102 and second Lewis acid gas are present (e.g., dissolved). The liquid can be any of a variety of liquids, such as water or an organic liquid (e.g., N,N-dimethylformamide, liquid quinone), an ionic liquid, a eutectic mixture of organic materials that are a particular combination of liquids, and combinations thereof. One example of a liquid quinone that may be suitable for the methods and systems herein is a liquid mixture of benzoquinone and a second quinone, such as naphthoquinone, as described in Shimizu A, Takenaka K, Handa N, Nokami T, Itoh T, Yoshida JI. Liquid Quinones for Solvent-Free Redox Flow Batteries. Advanced Materials. 2017 Nov;29(41):1606592, which is incorporated herein by reference for all purposes. In some embodiments, the liquid of the fluid mixture comprises a carbonate ester. For example, in some embodiments, the liquid comprises dimethyl carbonate, diethyl carbonate, ethyl-methyl carbonate, ethylene carbonate, propylene carbonate, or a combination thereof.

[0023] As previously mentioned, the fluid mixture can include a first Lewis acid gas. A Lewis acid gas generally refers to a gas species that can accept an electron pair from an electron pair donor (e.g., by having an empty orbital that is energetically accessible to the donor's electron pair). In some cases, the pK of the Lewis acid gas a is the pK of the electroactive species at one or more electrodes in the reduced state, if any. a For example, in some cases, the electroactive species has a pKa and optionally substituted quinones having a reduced state having a lower pK than the semiquinone. a In some embodiments, the first Lewis acid gas is sulfur dioxide (SO), sulfur oxide (SO), or the like. x ), nitric oxide (NO x ), R2S, carbonyl sulfide (COS), R3B, boron trifluoride (BF3), or combinations thereof (each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl). In some embodiments, R2S is hydrogen sulfide (HS). In some embodiments, R3B is borane. One example of a borane is BH3. For example, in some cases, the electroactive species has a pK a and optionally substituted quinones having a reduced state having a lower pK than the semiquinone. a In some embodiments, the first Lewis acid gas is sulfur dioxide (SO), sulfur oxide (SO), or the like. x ), nitric oxide (NO x ), RS, carbonyl sulfide (COS), R3B, boron trifluoride (BF3), or combinations thereof, where each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl. In some embodiments, the first Lewis acid gas is selected from sulfur dioxide (SO2), sulfur oxide (SO x ), nitric oxide (NO x), hydrogen sulfide (HS), carbonyl sulfide (COS), borane (BH), boron trifluoride (BF), or a combination thereof. In this context, a first Lewis acid gas that is a combination of two or more species should be understood to refer to a mixture containing each of the two or more species, and not a chemical product (e.g., an addition product) formed by a reaction between the two or more species. Those skilled in the art, having the benefit of this disclosure, will be able to readily identify the applicable SO x and NO x It can be understood that Lewis acid gases are understood, and that the "x" in these formulas refers to various stoichiometric coefficients. In some embodiments, the first Lewis acid is the species that is desired to be removed. For example, in certain carbon capture applications, sulfur-containing gases, such as SO2, may be present in a fluid stream (e.g., exhaust gas). The sulfur-containing gases may interfere with the carbon capture method (e.g., by competing with the sorbent material). Therefore, removing sulfur-containing species from the fluid mixture can improve the carbon capture process.

[0024] In some embodiments, the concentration of the first Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is relatively high. In some embodiments, the concentration of the first Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 0.00001 mole percent (mol%) or greater, 0.0001 mole percent (mol%) or greater, 0.001 mole percent (mol%) or greater, 0.01 mole percent (mol%) or greater, 0.1 mole percent (mol%) or greater, 0.5 mole percent or greater, 1 mole percent or greater, 5 mole percent or greater, 10 mole percent or greater, 25 mole percent or greater, 50 mole percent or greater, 75 mole percent or greater, 90 mole percent or greater, or greater. In some embodiments, the concentration of the first Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 99 mol% or less, 95 mol% or less, 90 mol% or less, 75 mol% or less, 50 mol% or less, 25 mol% or less, 10 mol% or less, 5 mol% or less, 2 mol% or less, 1 mol% or less, or less. Combinations (e.g., 0.01 mol% or more and 99 mol% or less) are possible. Another possible combination is 0.00001 mol% or more and 99 mol% or less.

[0025] In some embodiments, the concentration of the first Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 0.01 volume percent (v%) or more, 0.1 vol% or more, 0.5 vol% or more, 1 vol% or more, 5 vol% or more, 10 vol% or more, 25 vol% or more, 50 vol% or more, 75 vol% or more, 90 vol% or more, or more. In some embodiments, the concentration of the first Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 99 vol% or less, 95 vol% or less, 90 vol% or less, 75 vol% or less, 50 vol% or less, 25 vol% or less, 10 vol% or less, 10 vol% or less, 5 vol% or less, 2 vol% or less, 1 vol% or less, or less. Combinations are possible (eg, 0.01% or more by volume and 99% or less by volume).

[0026] In some embodiments, the fluid mixture includes a second Lewis acid gas. In some embodiments, the second Lewis acid gas includes one or more species selected from carbon dioxide, nitric oxide, RB, or RS (each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl). In some embodiments, the second Lewis acid gas includes one or more species selected from carbon dioxide, nitric oxide, borane, or HS. As previously mentioned, in some embodiments, the second Lewis acid gas is carbon dioxide, and it is desirable to subject the fluid mixture to a carbon capture or purification process (e.g., to produce substantially pure carbon dioxide for carbon sequestration). In some embodiments, RS is hydrogen sulfide (HS). Methods described herein, which involve removing a quantity of a first Lewis acid gas while removing essentially none or relatively little of any of the second Lewis acid gas (e.g., carbon dioxide) present in the fluid mixture, can be beneficial for some such applications. It should be understood that in some embodiments, the fluid mixture includes a first Lewis acid gas (e.g., SO) and two or more other Lewis acid gas species (e.g., CO and NO), and it is desirable to remove a certain amount of SO while removing essentially none or relatively little of the two or more other Lewis acid gas species (e.g., CO and NO). Another example of a Lewis acid gas that may be included in the second Lewis acid gas is NO. In such embodiments, the second Lewis acid gas is considered to be a combination (as a mixture) of two or more other Lewis acid gases (e.g., CO and NO). A further downstream step may then be performed in which a certain amount of one of the two or more other Lewis acid gases (e.g., NO) is removed (e.g., electrochemically) from the product fluid stream, while essentially none or relatively little of the other of the two or more other Lewis acid gases (e.g., CO). In some cases, the methods described herein involve removing a sulfur-containing Lewis acid gas while removing essentially no or relatively little of a second, different sulfur-containing Lewis acid gas.For example, in some embodiments, the first Lewis acid gas is SO and the second Lewis acid gas is HS, and the method includes removing an amount of SO from the fluid mixture while essentially none or relatively little HS is removed. As yet another example, in some cases, the methods described herein include removing a first borane while essentially none or relatively little a second, different borane. For example, in some embodiments, the first Lewis acid gas is BH and the second Lewis acid gas is BF, and the method includes removing an amount of BH from the fluid mixture while essentially none or relatively little BF is removed.

[0027] In some embodiments, the concentration of the second Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is relatively high, ie, the concentration of the second Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 0.01 mole percent (mol%) or greater, 0.1 mol% or greater, 0.5 mol% or greater, 1 mol% or greater, 5 mol% or greater, 10 mol% or greater, 25 mol% or greater, 50 mol% or greater, 75 mol% or greater, 90 mol% or greater, or greater. In some embodiments, the concentration of the second Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 99 mol% or less, 95 mol% or less, 90 mol% or less, 75 mol% or less, 50 mol% or less, 25 mol% or less, 10 mol% or less, 5 mol% or less, 2 mol% or less, 1 mol% or less, or less. Combinations (e.g., 0.01 mol% or more and 99 mol% or less) are possible.

[0028] In some embodiments, the concentration of the second Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 0.01 volume percent (v%) or more, 0.1 vol% or more, 0.5 vol% or more, 1 vol% or more, 5 vol% or more, 10 vol% or more, 25 vol% or more, 50 vol% or more, 75 vol% or more, 90 vol% or more, or more. In some embodiments, the concentration of the second Lewis acid gas in the fluid mixture (e.g., before the application of the potential difference) is 99 vol% or less, 95 vol% or less, 90 vol% or less, 75 vol% or less, 50 vol% or less, 25 vol% or less, 10 vol% or less, 10 vol% or less, 5 vol% or less, 2 vol% or less, 1 vol% or less, or less. Combinations are possible (eg, 0.01% or more by volume and 99% or less by volume).

[0029] In some embodiments, a relatively large amount of the first Lewis acid gas is removed from the fluid mixture during the processes described herein. Removal of a relatively large amount of the first Lewis acid gas can be beneficial for any of a variety of applications, such as capturing gases that, in some cases, could be harmful if released to the atmosphere for environmental reasons or harmful to downstream processes of the fluid mixture (e.g., carbon capture). In some embodiments, the amount of the first Lewis acid gas in the treated fluid mixture (e.g., a fluid mixture from which a quantity of the first Lewis acid gas has been exposed to an electrochemical cell and removed) is 50% or less, 25% or less, 10% or less, 5% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, or less (by volume percent) of the amount of the first Lewis acid gas in the original fluid mixture before treatment (e.g., the target amount in the fluid mixture before exposure to an electrochemical cell). In some embodiments, the amount of the first Lewis acid gas in the treated fluid mixture is 0.001% or more, 0.005%, 0.01% or more, 0.05%, 0.1%, 0.5%, 1%, 2%, 5%, or more (by volume percent) of the amount of the first Lewis acid gas in the original fluid mixture before treatment.

[0030] In some embodiments, the amount of the first Lewis acid gas in the treated fluid mixture (e.g., a fluid from which an amount of the first Lewis acid gas has been exposed to an electrochemical cell and removed) is 50% or less, 25% or less, 10% or less, 5% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, or less (mol percent) of the amount of the first Lewis acid gas in the original fluid mixture before separation (e.g., the target amount in the fluid mixture before exposure to the electrochemical cell). In some embodiments, the amount of the first Lewis acid gas in the treated fluid mixture is 0.001% or more, 0.005%, 0.01% or more, 0.05%, 0.1%, 0.5%, 1%, 2%, 5%, or more (mol percent) of the amount of the first Lewis acid gas in the original fluid mixture before treatment.

[0031] As previously mentioned, certain electroactive species may be used during the methods described herein to remove a certain amount of a first Lewis acid gas, but essentially none or relatively little of a second Lewis acid gas. As used herein, electroactive species generally refers to an agent (e.g., a chemical entity) that undergoes oxidation or reduction upon exposure to an electric potential in an electrochemical cell. However, it should be understood that electroactive species can undergo electric potential-induced oxidation and reduction reactions, as well as chemically induced changes in oxidation state (e.g., by exposure to chemical reducing or oxidizing agents in solution or on a surface). In some, but not necessarily all, embodiments, an electrode comprises an electroactive species. When an electrode comprises an electroactive species, it should be understood that the electroactive species can be located on the surface of the electrode, at least partially within the electrode (e.g., in the pores of the electrode), or both. For example, referring to FIG. 2, in some embodiments, an electrochemical cell 100 comprises a negative electrode 110, and the negative electrode 110 comprises an electroactive species. The electroactive species may be present on or near the surface of the negative electrode 110, the electroactive species may be present within at least a portion of the negative electrode 110, or a combination of both. In some embodiments, some or all of the electroactive species are not part of the electrode. Instead, in some embodiments, the electroactive species is present in a conductive medium, such as an electrolyte (e.g., a liquid electrolyte solution). In some such embodiments, the electroactive species may be freely diffusible in the conductive medium (e.g., dissolved in a conductive liquid, such as a liquid electrolyte solution).

[0032] As used herein, the negative electrode of an electrochemical cell refers to the electrode into which electrons are injected during the charging process. For example, with reference to Figure 2, when electrochemical cell 100 is charged (e.g., by application of an electric potential by an external power source), electrons travel through an external circuit (not shown) to negative electrode 110. Thus, in some cases, species in electronic communication with the negative electrode can be reduced to a reduced state (a state with an increased number of electrons) during the charging process of the electrochemical cell.

[0033] An electroactive species can have an oxidized state (fewer electrons than the reduced state) and at least one reduced state (more electrons than the oxidized state) in at least one conductive medium. As a non-limiting example, if the electroactive species is an optionally substituted quinone, the neutral quinone can be considered an oxidized state, the semiquinone (the product of adding one electron to the neutral quinone) can be considered one reduced state, and the quinone dianion (the product of adding one electron to the neutral quinone) can be considered another reduced state.

[0034] In some embodiments, the electroactive species has at least one reduced state capable of combining with a first Lewis acid gas (e.g., SO2) in at least one conductive medium. A species capable of combining with a first Lewis acid gas generally refers to the species' ability to undergo a combining reaction with a first Lewis acid gas to a degree and at a rate significantly sufficient for a useful gas capture and / or separation process to occur. For example, a species capable of combining with a first Lewis acid gas may have a reduced state capable of combining with a first Lewis acid gas at room temperature (23°C) of 10 1 M -1 or greater, 10 2 M -1 or greater and / or 10 3 M -1The species may have a binding constant with the first Lewis acid gas of up to or greater than 1000 kJ / s. The species capable of binding with the first Lewis acid gas may be able to bind with the first Lewis acid gas on a time scale of minutes, seconds, milliseconds, or even just microseconds, or less. The species may be able to bind with the Lewis acid gas at at least one temperature (e.g., at least one temperature greater than 223 K and less than 573 K, e.g., 298 K). In some embodiments, the species may be able to bind with the Lewis acid gas at a first temperature, but binding with the Lewis acid gas at a second temperature is thermodynamically and / or kinetically unfavorable. Such temperature dependence may be based on the temperature dependence of the change in Gibbs free energy between the species (e.g., reduced quinone) and the Lewis acid gas (e.g., carbon dioxide). Using the insights and guidance of the present disclosure, one skilled in the art can select a suitable temperature to promote binding between at least one reduced state species and the Lewis acid gas (e.g., the first Lewis acid gas).

[0035] In some embodiments, the electroactive species has an oxidized state capable of releasing a bound first Lewis acid gas in at least one conductive medium. The electroactive species may be selected to have a strong affinity for the Lewis acid gas in at least one reduced state for the particular application for which it is intended. For example, in some embodiments where SO2 is the first Lewis acid gas, the selected electroactive species may have a 10% affinity for SO2. 1 ~10 3 M -1 In some embodiments, the selected electroactive species can have a binding constant of 10 with a different first Lewis acid gas. 1 ~10 3 M -1It has been observed that some, but not all, quinones can be used as suitable electroactive species. In some embodiments, in the presence of SO, an optionally substituted quinone can be reduced (e.g., in a single step or multiple steps) to its semiquinone or dianion, which then binds to SO to form a complex. Other electroactive species capable of forming a covalent bond with a first Lewis acid gas (SO) upon reduction can also be used.

[0036] In some embodiments, the electroactive species has at least one reduced state in at least one electrically conductive medium at which the species can combine with a first Lewis acid gas, but there is at least one temperature (e.g., 298 K) at which it is thermodynamically unfavorable for the species to react with a second Lewis acid gas. In some embodiments, the electroactive species has at least one reduced state at which the species can combine with a first Lewis acid gas, but there is at least one temperature at which it is thermodynamically unfavorable for the species to react with a second Lewis acid gas at at least one temperature in the range of 223 K or greater, 248 K or greater, 273 K or greater, 298 K or greater, and / or up to 323 K, 348 K, 373 K, 398 K, 423 K, 448 K, 473 K, 498 K, 523 K, 548 K, 573 K, or higher. In some embodiments, the electroactive species has at least one reduced state in which the species can combine with a first Lewis acid gas, but it is thermodynamically unfavorable for the species to react with a second Lewis acid gas at a temperature of 298 K. As used herein, a reaction that is thermodynamically unfavorable at a given temperature refers to a reaction that has a positive change in Gibbs free energy (ΔG rxnFor example, a reaction between at least one reduced species and a second Lewis acid gas (e.g., CO) may have a Gibbs free energy change (ΔG) of greater than 0 kcal / mol, +0.1 kcal / mol or greater, +0.5 kcal / mol or greater, +1 kcal / mol or greater, +2 kcal / mol or greater, +3 kcal / mol or greater, +5 kcal / mol or greater, and / or up to +8 kcal / mol, +10 kcal / mol, +20 kcal / mol, or greater, at at least one temperature in the range of 223 K or greater, 248 K or greater, 273 K or greater, 298 K or greater, and / or up to 323 K, 348 K, 373 K, 473 K, 573 K, or higher. rxn In some embodiments, the reaction between the at least one reduced state species and a second Lewis acid gas (e.g., CO) may have a change in Gibbs free energy (ΔG) of greater than 0 kcal / mol, greater than or equal to +0.1 kcal / mol, greater than or equal to +0.5 kcal / mol, greater than or equal to +1 kcal / mol, greater than or equal to +2 kcal / mol, greater than or equal to +3 kcal / mol, greater than or equal to +5 kcal / mol, and / or up to +8 kcal / mol, up to +10 kcal / mol, up to +20 kcal / mol, or greater, at a temperature of 298 K. rxn )

[0037] In certain cases, the electroactive species has at least one reduced state in at least one conductive medium at which the species can combine with a first Lewis acid gas, but at least one temperature (e.g., 298 K) exists at which it is kinetically unfavorable for the species to combine with a second Lewis acid gas because the reaction rate is too slow to occur on a time scale commensurate with the time scale characteristic of the process / process step (e.g., gas capture), such as microseconds, milliseconds, seconds, or minutes. It has been found that such kinetic selectivity can be achieved in various ways, including functionalizing the electroactive species with certain substituents. For example, the electroactive species can be functionalized with bulky substituents (e.g., tert-butyl moieties) so that steric hindrance hinders the reaction of the species with the second Lewis acid gas to a greater extent than steric hindrance hinders the reaction of the species with the first Lewis acid gas.

[0038] In some embodiments in which the electroactive species has at least one reduced state at which it can combine with a first Lewis acid gas, but there is at least one temperature (e.g., 298 K) at which combining with a second Lewis acid gas is kinetically unfavorable, the ratio of the rate constant for reaction of the species with the first Lewis acid gas to the rate constant for reaction with the second Lewis acid gas is 2 or greater, 5 or greater, 10 or greater, 50 or greater, 100 or greater, and / or up to 500, up to 1000, or greater. In some embodiments where the electroactive species has at least one reduced state at which it can combine with a first Lewis acid gas, but at least one temperature exists where combining with a second Lewis acid gas is kinetically unfavorable (e.g., 298 K), the ratio of the time scale of the reaction of the species with the first Lewis acid gas to the time scale of the second Lewis acid gas is 2 or greater, 5 or greater, 10 or greater, 50 or greater, 100 or greater, and / or up to 500, 1000, or greater. The ratio of the time scales of the reactions of the first Lewis acid gas and the species with the second Lewis acid gas can be determined by measuring the time to 50% completion for each reaction, each reaction being carried out under otherwise essentially identical conditions (same initial gas concentrations, same temperature, same concentrations, same reaction medium (e.g., solvent and supporting electrolyte, if present), same mixing rate, same concentration and / or available surface area of ​​the electroactive species, etc.). For example, one of ordinary skill in the art having the benefit of this disclosure can use cyclic voltammetry in a conductive medium (with the conductive medium saturated with a Lewis acid gas) to determine whether a reaction between a species and a Lewis acid gas is thermodynamically and / or kinetically favored or unfavorable.

[0039] pK of electroactive species in the reduced state aIt is believed that the pK of the first Lewis acid gas and the second Lewis acid gas may at least partially contribute to modulating the selectivity of the species with respect to the first Lewis acid gas and the second Lewis acid gas. In some embodiments, in at least one reduced state, the electroactive species has a pK of the first Lewis acid gas. a or greater than the pK of the second Lewis acid gas a Less than pK a As a non-limiting example, in some embodiments, in at least one reduced state, the electroactive species has a pKa of SO or greater and less than the pKa of CO in at least one conductive medium or in the conductive medium of the process being performed. a By judiciously selecting the pKa of the reduced state electroactive species (e.g., by derivatization with a functional group), selective reactivity of a first Lewis acid gas relative to a second Lewis acid gas can be achieved. One skilled in the art can determine the pKa of an electroactive species (e.g., in its reduced state) by chemically or electrochemically preparing the reduced state and performing an acid-base titration (e.g., colorimetrically, by cyclic voltammetry, etc.) or any other suitable technique known in the art. a The relative pK of a species under given conditions (temperature, solvent, supporting electrolyte) can be determined. a The pK value can be determined using electrochemical techniques, such as cyclic voltammetry or open circuit potential techniques, to determine the reduction potential of the species, with species having a more positive reduction potential having a lower pK a pK a may depend on the temperature at which it is measured. a is measured at one of the temperatures listed above, for example 298K.

[0040] In some cases, at least one reduced state electroactive species may be capable of reacting with both a first Lewis acid gas and a second Lewis acid gas at a first temperature, but at a second, different temperature, the at least one reduced state electroactive species may combine with the first Lewis acid gas, but reaction with the second Lewis acid gas is thermodynamically and / or kinetically unfavorable. In some such cases, removing a quantity of a first Lewis acid gas from a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas may include combining the first Lewis acid gas with one or more electroactive species in a reduced state and combining the second Lewis acid gas with one or more electroactive species in a reduced state at the first temperature to form a first Lewis acid gas-electroactive species complex and a second Lewis acid gas-electroactive species complex, respectively. The first Lewis acid gas-electroactive species composite and the second Lewis acid gas-electroactive species composite can then be exposed to conditions at a second, different temperature that reverse the binding reaction between the second Lewis acid gas and the electroactive species, thereby releasing an amount (e.g., at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, at least 98%, at least 99%, or all, by mole percent or volume percent) of the second Lewis acid gas from the composite, while releasing essentially none or relatively little (e.g., 10% or less, 5% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, and / or as little as 0.05%, as little as 0.01%, or less, by mole percent or volume percent) of the first Lewis acid gas. The change from the first temperature to the second temperature can cause at least partial release by shifting the equilibrium constant for the respective binding reaction in a way that allows the gas to be released.For example, the binding reactions that form the complex can each have a negative Gibbs free energy change at a first temperature, but at a second temperature, the reaction involving the binding of a first Lewis acid gas can remain negative, while the reaction involving the binding of a second Lewis acid can become positive (and thus thermodynamically unfavorable). Judicious selection of electroactive species can be used to achieve such effects based on various considerations. For example, the electroactive species can be selected based on knowledge or measurement of the enthalpy change and entropy change for each reaction that forms a complex with the electroactive species.

[0041] One non-limiting way in which a first Lewis acid gas can be removed from a fluid mixture while removing little or essentially no second Lewis acid gas (e.g., carbon dioxide) is by applying a certain potential across an electrochemical cell during at least a portion of operation. For example, it has been discovered in the context of the present disclosure that it is possible to apply a potential across the electrochemical cell (e.g., a first potential) sufficient to reduce an electroactive species to at least one reduced state capable of binding to a first Lewis acid gas, but that the potential is insufficient to reach a state in which the species (or the electrode itself) can react with (e.g., bind to) a second Lewis acid gas. While judicious selection of the electroactive species may make it possible to apply such a potential, certain conventional electroactive species may not allow such a potential to be applied. The potential applied across the electrochemical cell can be such that the electrode potential of the negative electrode is positive (e.g., 10 mV or more, 50 mV or more, 100 mV or more, 200 mV or more, 5 mV or more, and / or up to 1 V or more) relative to the standard reduction potential for forming a reduced state species capable of binding to a second Lewis acid gas.

[0042] While certain embodiments described above relate to selectively removing a first Lewis acid gas from a mixture comprising a first Lewis acid gas and a second Lewis acid gas by selectively reacting the first Lewis acid gas with an electroactive species to a greater extent than the second Lewis acid gas, other methods of selectively removing a first Lewis acid gas are also contemplated. By way of example, some embodiments relate to a method that includes selectively removing a Lewis acid gas by combining a first Lewis acid gas (e.g., sulfur dioxide) and a second Lewis acid gas (e.g., carbon dioxide) with one or more reduced electroactive species, and then selectively releasing the second Lewis acid gas from the composite (e.g., by oxidation of the second Lewis acid gas-electroactive species composite) while releasing relatively little or none of the first Lewis acid gas from the composite.

[0043] In some embodiments, a fluid mixture containing a first Lewis acid gas and a second Lewis acid gas is exposed to one or more electroactive species. The electroactive species (e.g., an optionally substituted quinone) can be in a reduced state (e.g., an optionally substituted semiquinone, an optionally substituted quinone dianion, or a combination thereof). For example, referring to FIG. 3 , a fluid mixture 101 containing a first Lewis acid gas 102 and a second Lewis acid gas 104 can be exposed to a reduced electroactive species R. The electroactive species can initially be in an oxidized state (e.g., an optionally substituted quinone) and then converted to a reduced state (e.g., an optionally substituted semiquinone or quinone dianion). Such a reduction process to prepare the reduced state electroactive species can occur before and / or during the step of exposing the fluid mixture containing the first Lewis acid gas and the second Lewis acid gas to the electroactive species. The reduction can occur, for example, by electron transfer upon application of a potential difference across an electrochemical cell including a negative electrode in electronic communication with the electroactive species. The reduced state electroactive species can be part of an electrode (e.g., immobilized on a negative electrode), can be freely diffusing in a liquid solution (e.g., a fluid mixture), or a combination thereof.

[0044] Exposure to one or more electroactive species in a reduced state can include, for example, flowing a fluid mixture up to or through (e.g., in proximity to) the electroactive species and / or mixing a Lewis acid gas with the electroactive species in solution (e.g., by mixing a separate solution containing the electroactive species with a gas mixture including a Lewis acid gas or bubbling a gas mixture including a Lewis acid gas through a solution containing the electroactive species).

[0045] In some embodiments, a quantity of a first Lewis acid gas is bound to a first portion of the electroactive species in a reduced state to form a first Lewis acid gas-electroactive species composite. Furthermore, in some embodiments, a quantity of a second Lewis acid gas is bound to a second portion of the electroactive species in a reduced state to form a second Lewis acid gas-electroactive species composite. The binding of the first Lewis acid gas to the first portion of the electroactive species and the binding of the second Lewis acid gas to the second portion of the electroactive species can occur simultaneously or sequentially. For example, in some embodiments, the second Lewis acid gas can be bound to the reduced electroactive species (e.g., a subset or all of the electroactive species), and then, after a period of time, the first Lewis acid gas can be bound to the reduced electroactive species (e.g., a subset or all of the electroactive species). In other embodiments, the first Lewis acid gas and the second Lewis acid gas are each bound to the reduced electroactive species during the same period of time. It should be understood that the Lewis acid gas-electroactive species complex can be formed by any of a variety of forces, such as covalent, ionic, hydrogen bonding, or specific non-covalent affinity interactions. Referring again to Figure 3, according to certain embodiments, a first Lewis acid gas molecule 102 (e.g., sulfur dioxide) can bind to a reduced electroactive species R to form a first Lewis acid gas-electroactive species complex 107, and a second Lewis acid gas molecule 104 (e.g., carbon dioxide) can bind to a reduced electroactive species R to form a second Lewis acid gas-electroactive species complex 109. Once complexed, the first and second Lewis acid gases can be at least temporarily immobilized to the structure of the device (e.g., an electrode) or to the solution in which the electroactive species are present (e.g., dissolved). The one or more first portions of the electroactive species (to which the first Lewis acid gas is bound) can be, for example, a first plurality of electroactive species molecules or polymer moieties, and the second portion of the electroactive species (to which the second Lewis acid gas is bound) can be a second plurality of electroactive species molecules or polymer moieties.The one or more first portions of electroactive species and the one or more second portions of electroactive species can be the same type of species (e.g., the same type of optionally substituted quinone molecule or polymer residue), or the first portion and second portion can comprise different types of species (e.g., quinones with different substituents).

[0046] In some embodiments, at least a portion of the second Lewis acid gas-electroactive species complex is oxidized such that an amount (e.g., at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, at least 98%, at least 99%, or all) of the second Lewis acid gas is released from the complex. For example, referring again to FIG. 3 , the second Lewis acid gas-electroactive species complex 109 may be oxidized during step 10 to form electroactive species in their oxidized state Ox, thereby releasing second Lewis acid gas molecules 104 from the second Lewis acid gas-electroactive species complex 109. The released second Lewis acid gas molecules (e.g., carbon dioxide) may then, in some cases, be separated from the fluid mixture containing the first Lewis acid gas-electroactive species complex (e.g., sulfur dioxide-electroactive species complex). Such separation can be achieved in some cases where the composite is immobilized by flowing a fluid mixture through the immobilized composite (e.g., by flowing a gas or fluid stream using a positive and / or negative pressure source). In some cases where the composite is at least partially dissolved in solution, the second Lewis acid gas can be separated by degassing the second Lewis acid gas or by evaporation (e.g., by exposure to reducing conditions, e.g., vacuum). Oxidation of the second Lewis acid gas-electroactive species composite can be carried out using any of a variety of techniques, such as electrochemical or chemical techniques. For example, the oxidation step can include exposing the second Lewis acid gas-electroactive species composite to an electrochemical cell while simultaneously applying a potential difference across the electrochemical cell. The second Lewis acid gas-electroactive species composite can be exposed to the negative electrode of the electrochemical cell, for example, as a free composite in solution (under diffusion or forced fluid flow), or the electroactive species can be immobilized to the negative electrode (e.g., by adsorption, functionalization, or inclusion in a redox-active polymer). Alternatively or additionally, oxidation may involve exposure to a suitable chemical oxidizing agent, either dissolved in solution or immobilized / deposited on a surface.

[0047] In some embodiments, at least a portion of the second Lewis acid gas-electroactive species complex is oxidized (a certain amount of the second Lewis acid gas is released), while essentially no first Lewis acid gas is released from the first Lewis acid gas-electroactive species complex (e.g., a very small amount relative to the intended application). In some embodiments, at least a portion of the second Lewis acid gas-electroactive species complex is oxidized (a certain amount of the second Lewis acid gas is released), while 70% or less, 50% or less, 25% or less, 10% or less, 5% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, 0.05% or less, and / or only 0.01%, only 0.001%, or less of the first Lewis acid gas of the first Lewis acid gas-electroactive species complex is released, by mole percent. Essentially no or relatively little first Lewis acid gas may be released during the oxidation of the second Lewis acid gas-electroactive species complex for any of a variety of reasons. For example, the oxidizing power of an oxidant (e.g., a chemical oxidant or an electrode at a given potential) may be sufficient to oxidize the second Lewis acid gas-electroactive species complex (e.g., thermodynamically or kinetically) but insufficient to oxidize the first Lewis acid gas-electroactive species complex, so that conditions under which oxidation of the second Lewis acid gas-electroactive species complex occurs may not result in oxidation of the first Lewis acid gas-electroactive species complex. Such an occurrence may occur when different complexes have different oxidation potentials under given conditions, and the acidity may be due to the different acidities of the first and second Lewis acid gases. Another example is one in which the conditions under which oxidation of the second Lewis acid gas-electroactive species complex occurs result in at least partial oxidation of the first Lewis acid gas-electroactive species complex, but the affinity between the first Lewis acid gas and the oxidized state of the electroactive species is strong enough so that the complex is maintained and the first Lewis acid gas is not released. To employ any of the aforementioned techniques, judicious selection of oxidizing agent / potential and / or electroactive species (e.g., measured reduction potentials and / or pK values ​​of the electroactive species and Lewis acid gas) is essential. avalue) can be used.

[0048] In some embodiments, the step of oxidizing the second Lewis acid gas-electroactive species complex is performed multiple times. For example, the gases released during the oxidation step (e.g., the released second Lewis acid gas and a relatively small amount of the first Lewis acid gas) can be separated from the fluid mixture and exposed to a second set of reduced electroactive species (e.g., in a second electrochemical cell) to form new second Lewis acid gas-electroactive species complexes and first Lewis acid gas-electroactive species, where the ratio of the first Lewis acid gas to the second Lewis acid gas is higher than during the initial exposure step of the process. The new second Lewis acid gas-electroactive species can then be oxidized to release the second Lewis acid gas from the complex while releasing essentially no, or a relatively small amount of, the first Lewis acid gas from the complex. This process can be repeated two, three, four, or more times, each time progressively enriching the fluid mixture with the second Lewis acid gas while depleting the fluid mixture of the first Lewis acid gas. Such sequential processes can be carried out, for example, using a distillation-type apparatus having multiple trays.

[0049] In some embodiments, the first Lewis acid gas-electroactive species complex is oxidized to release an amount (e.g., at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, at least 98%, at least 99%, or all) of the first Lewis acid gas by mole percent or by volume percent. Such release of the first Lewis acid gas (e.g., sulfur dioxide) can occur after separation from the second Lewis acid gas (e.g., carbon dioxide). In some embodiments, oxidation of the first Lewis acid gas-electroactive species complex occurs after oxidation of the second Lewis acid gas-electroactive species complex. By way of example, in some embodiments, oxidation of the second Lewis acid gas-electroactive species complex is a first oxidation step carried out during a first period of time, and a second oxidation step comprising oxidizing at least a portion of the first Lewis acid gas-electroactive species complex is carried out during a second (e.g., subsequent) period of time such that an amount of the first Lewis acid gas is released. Referring again to FIG. 3, the first Lewis acid gas-electroactive species compounds 107 may be oxidized during step 20 to form electroactive species in their oxidized state Ox, thereby releasing first Lewis acid gas molecules 102.

[0050] The second oxidation step can be carried out electrochemically or chemically, as in the case of the first oxidation step. For example, the second oxidation step can include exposing the second Lewis acid gas-electroactive species composite to the electrochemical cell while simultaneously applying a potential difference across the electrochemical cell. In some embodiments, the electrochemical cell used for the second oxidation step is the same electrochemical cell as the first oxidation step. For example, the second Lewis acid gas-electroactive species composite can be oxidized at the negative electrode of the electrochemical cell for a first period of time, and then the first Lewis acid gas-electroactive species composite can be oxidized at the same negative electrode for a second period of time. By using different potentials for different times, different oxidations can be performed at different times. For example, a first potential difference can be applied during the first oxidation step that is sufficient to oxidize the second Lewis acid gas-electroactive species composite but insufficient (e.g., thermodynamically) to oxidize the first Lewis acid gas-electroactive species composite. Then, during a second oxidation step, a second potential difference can be applied that is sufficient to oxidize the first Lewis acid gas-electroactive species complex.

[0051] Alternatively, the first and second oxidations can be performed in different electrochemical cells (e.g., of a gas separation system). For example, the first oxidation step can involve exposing the second Lewis acid gas-electroactive species complex to a first electrochemical cell while simultaneously applying a potential difference across the first electrochemical cell, and the second oxidation step can involve exposing the first Lewis acid gas-electroactive species complex to a second (different) electrochemical cell while simultaneously applying a potential difference across the second electrochemical cell. The second potential difference can be different from the first potential difference (e.g., resulting in a more positive potential at the negative electrode). Such a process can be performed, for example, using a redox flow apparatus. FIG. 4 shows a schematic diagram of an exemplary flow apparatus 400 including a first electrochemical cell 100 and a second electrochemical cell 200. The first electrochemical cell 100 and the second electrochemical cell 200 can each include an anode 110. The anodes 110 may each be in fluid communication with a conduit 402 configured to flow a fluid mixture (e.g., a gas-fluid mixture or a liquid solution). That is, the fluid in the conduit may be able to contact at least one surface of the anode of the first electrochemical cell and the anode of the second electrochemical cell. In the embodiment shown in FIG. 4, the fluidic device 400 may be configured to receive a fluid mixture 405 (e.g., from a fluid mixture source) via an inlet, and the anode 110 of the first electrochemical cell 100 may be arranged with a conduit such that the flow of the fluid mixture 405 may expose the fluid mixture 405 to the anode 110 of the first electrochemical cell 100. In the first electrochemical cell 100, the oxidation step 10 shown in FIG. 3 may be performed to oxidize the second Lewis acid gas-electroactive species complex such that an amount of the second Lewis acid gas is released. Intermediate outlet 403 may be positioned and configured to receive a second Lewis acid gas 407 that has been separated from fluid mixture 405 (e.g., by connection to a vacuum source). Flow device 406 may be configured to transport the resulting fluid mixture 406, including the first Lewis acid gas-electroactive species, to second electrochemical cell 200, but at least partially (or completely) depleted of the second Lewis acid gas molecules.A conduit 402 may be arranged at the anode 110 of the second electrochemical cell 200 such that the flow of the fluid mixture 406 may expose the fluid mixture 406 to the anode 110 of the second electrochemical cell 200. In the second electrochemical cell 200, the oxidation step 20 shown in Figure 3 may be performed to oxidize the first Lewis acid gas-electroactive species complex such that an amount of the first Lewis acid gas is released. The flow device 400 may further be configured to exhaust the released first Lewis acid (e.g., as gas 408 from an outlet).

[0052] As a non-limiting example of the aforementioned process, sulfur dioxide and carbon dioxide are each reacted with para-naphthoquinone dianion (p-NQ) dissolved in an organic liquid. 2- ) (e.g., by bubbling a gas through the liquid). The para-naphthoquinone dianion can be prepared by electrochemical or chemical reduction. This exposure can result in the formation of p-NQ(SO2)2 and p-NQ(CO2)2 complexes in solution. The solution can then be exposed to the negative electrode of an electrochemical cell during application of an oxidizing potential sufficient to oxidize p-NQ(CO2)2 to form the neutral species p-NQ and CO2, but insufficient to oxidize the p-NQ(SO2)2 complexes in solution. The released CO2 can be removed from the solution (e.g., as part of a fluid mixture, e.g., a gas mixture for further downstream processing, e.g., carbon capture). The remaining solution containing p-NQ(SO2)2 can then be exposed to a negative electrode (either the same electrode or an electrode of a second electrochemical cell) during application of a more positive oxidizing potential sufficient to oxidize the p-NQ(SO2)2, now separated from CO2, to form p-NQ and SO2.

[0053] The electroactive species described herein may be in any suitable form, provided that it satisfies at least one of the criteria required herein. In some embodiments, the electroactive species is or includes a molecular species. For example, the electroactive species may be or include an organic molecule. The electroactive species may include one or more functional groups capable of binding to a first Lewis acid gas in the fluid mixture (e.g., when the electroactive species is in a reduced state). The functional group may include, for example, a carbonyl group. In some embodiments, the electroactive species is part of a polymer, e.g., a redox-active polymer. The electroactive species may be part of a polymer material immobilized on the negative electrode. For example, referring to FIG. 2, the electroactive species may be part of a polymer material immobilized on the negative electrode 110 of the electrochemical cell 100. However, as previously mentioned, the electroactive species may be present in a conductive medium (e.g., a conductive liquid).

[0054] In some embodiments, the electroactive species is or comprises an organic species. The species may be optionally substituted (i.e., the species may include functional groups and / or other moieties or linkages attached to the main structure of the species). In some embodiments, the organic species comprises one or more species selected from optionally substituted quinones, optionally substituted thiolates, optionally substituted bipyridines, optionally substituted phenazines, and optionally substituted phenothiazines.

[0055] In certain cases, the electroactive species is or comprises a redox-active polymer that includes an optionally substituted organic species. The selection of substituents (e.g., functional groups) on the optionally substituted species can be determined by, but not limited to, the pK aThe effect of the optionally substituted species on the standard reduction potential of the optionally substituted species may depend on any of a variety of factors, including its effect on the standard reduction potential of the optionally substituted species, and / or the standard reduction potential of the optionally substituted species. Those skilled in the art, having the benefit of this disclosure, will be able to determine which substituents or combinations of substituents on an optionally substituted species (e.g., quinone) are suitable for electroactive species, for example, based on synthetic feasibility, as well as the resulting pK a and / or standard reduction potentials.

[0056] As a non-limiting example, substitution of certain quinones with electron-withdrawing groups can modulate the electron density of certain redox states of the quinone (e.g., the pK of the reduced state), which can affect the selectivity of the species for Lewis acid gases. a As a non-limiting example, 1,4-naphthoquinone can be substituted with an electron-withdrawing group (e.g., 2,3-dicyano-1,4-napthoquinone) to form an electron-withdrawing group (e.g., 2,3-dicyano-1,4-napthoquinone). It has been unexpectedly observed that functionalization with a Lewis acid gas (nitrile of Lewis acid gas) can impart selectivity for the binding of SO over the binding of CO upon reduction. One skilled in the art with the benefit of this insight can screen potential electroactive species for the desired selectivity of Lewis acid gases by performing cyclic voltammetry and / or thermogravimetric analysis of the electroactive species in the presence of each Lewis acid gas at the desired temperature in the desired conductive liquid to determine the relative reactivity.

[0057] In some embodiments, the optionally substituted quinone is or includes an optionally substituted naphthoquinone. In certain cases, the optionally substituted quinone is or includes an optionally substituted anthraquinone. In some embodiments, the optionally substituted quinone is or includes an optionally substituted quinoline. In some embodiments, the optionally substituted quinone is or includes an optionally substituted thiochromene-dione. In some embodiments, the optionally substituted quinone is benzo[g]quinoline-5,10-dione, benzo[g]isoquinoline-5,10-dione, benzo[g]quinoxaline-5,10-dione, quinoline-5,8-dione, or 1-lambda 4 -thiochromene-5,8-dione. In some embodiments, the optionally substituted quinone is or includes an optionally substituted phenanthrenequinone (also called an optionally substituted phenanthrene dione). The substituents (e.g., functional groups) can be any of those listed above or below.

[0058] As mentioned above, the electroactive species can be part of a redox-active polymer. In some cases, any of the optionally substituted species (e.g., organic species) described herein can be part of a redox-active polymer. In some such cases, at least a portion of the redox-active polymer comprises a backbone and one or more optionally substituted species covalently bonded to the backbone. The backbone generally refers to the longest series of covalently bonded atoms that together create a continuous chain of polymer molecules. In certain other cases, the optionally substituted species described herein can be part of the backbone of the redox-active polymer.

[0059] The electroactive species may comprise a crosslinked polymeric material. For example, in some embodiments, the electroactive species comprises or is incorporated into a hydrogel, an ionogel, an organogel, or a combination thereof. Such crosslinked polymeric materials are generally known in the art and, in some cases, may include the electroactive species described herein as part of their three-dimensional structure (e.g., by covalent bonding). However, in some embodiments, the electroactive species is incorporated into the crosslinked polymeric material by adsorption (e.g., physisorption and / or chemisorption). In some embodiments, the electroactive species comprises an extended network. For example, The electroactive species may include a metal-organic framework (MOF) or a covalent organic framework (COF). In some embodiments, the electroactive species includes a functionalized carbonaceous material. For example, the electroactive species may include functionalized graphene, functionalized carbon nanotubes, functionalized carbon nanoribbons, edge-functionalized graphite, or a combination thereof.

[0060] Exemplary functional groups with which the optionally substituted quinone may be functionalized include, but are not limited to, halo (e.g., chloro, bromo, iodo), hydroxyl, carboxylate / carboxylic acid, sulfonate / sulfonic acid, alkylsulfonate / alkylsulfonic acid, phosphonate / phosphonic acid, alkylphosphonate / alkylphosphonic acid, acyl (e.g., acetyl, ethyl ester, etc.), amino, amido, quaternary ammonium (e.g., tetraalkylamino), branched or unbranched alkyl (e.g., C1-C18 alkyl), heteroalkyl, alkoxy, glycoxy, polyalkylene glycoxy (e.g., polyethylene glycoxy), imino, polyimino, branched or unbranched alkenyl, branched or unbranched alkynyl, aryl, heteroaryl, heterocyclyl, nitro, nitrile, thiyl, and / or carbonyl groups (any of which may be optionally substituted). The aforementioned functional groups can also be used in any of the other types of electroactive species described herein (e.g., optionally substituted thiolates, optionally substituted bipyridines, optionally substituted phenazines, and optionally substituted phenothiazines, functionalized hydrogels, functionalized carbonaceous materials such as functionalized graphene, functionalized carbon nanotubes, edge-functionalized graphite, etc.). As can be appreciated by those skilled in the art, the heteroaryl substituent of an aromatic species such as a quinone can be a ring fused to the aromatic species. For example, a quinone functionalized with a heteroaryl group can be a quinoline-dione (e.g., benzoquinoline-dione). The heteroatom in the ring that is part of the electroactive species can, in some cases, affect the pK of the reduced form of the electroactive species. a and / or affect its standard reduction potential. For example, a quinoline-diones may have a more positive standard reduction potential than a naphthoquinone, and a quinoxaline-diones may have a more positive standard reduction potential than a quinoline-diones.

[0061] In certain aspects, electrochemical devices are generally described. Figure 2 illustrates, as one such example, an electrochemical device 105 according to certain embodiments. The electrochemical device may, in some cases, be configured to perform the methods described herein.

[0062] In some embodiments, the electrochemical device includes a chamber including a negative electrode. For example, in some embodiments, the electrochemical device 105 includes a chamber 103 and an electrochemical cell 100, which includes a negative electrode 110. The chamber can be constructed to receive a fluid mixture. In some cases, the chamber of the electrochemical device is configured to allow the fluid mixture to enter the chamber and, in some cases, exit the chamber. For example, in some embodiments, the chamber includes a fluid inlet and a fluid outlet. Referring again to FIG. 2, in some embodiments, the electrochemical device 105 includes a chamber 103 including a fluid inlet 106 and a fluid outlet 108. Thus, one or more of the methods described herein can be performed by flowing a fluid mixture 101 (e.g., including a first Lewis acid gas and a second Lewis acid gas) into the chamber 103 via the fluid inlet 106, thereby exposing at least a portion of the fluid mixture to the electrochemical cell (e.g., including the negative electrode 110). The electrochemical cell may be equipped with an external circuit and power source (e.g., coupled to a potentiostat) to enable application of a potential difference. The electrochemical device may be configured so that at least a portion of the fluid mixture can be transported out of the chamber via a fluid outlet (e.g., fluid outlet 108 of FIG. 2). In some embodiments, the fluid inlet is fluidly connected to a fluid mixture source (e.g., a mixture source including a first Lewis acid gas and a second Lewis acid gas). In some embodiments, the fluid outlet is fluidly connected to a downstream device for further processing (e.g., another electrochemical device for removing another Lewis acid gas). In some embodiments, the electrochemical device includes multiple chambers (e.g., each including a negative electrode) fluidly connected in series.

[0063] In some embodiments, the electrochemical device includes an electroactive species in electronic communication with a negative electrode. For example, referring again to FIG. 2 , in some embodiments, an electroactive species (not shown) is in electronic communication with the negative electrode 110. Electronic communication, in this context, generally refers to the ability to undergo electron transfer reactions by either outer-sphere (electron / hole transfer) or inner-sphere (bond-breaking and / or bond-forming) mechanisms. In some embodiments in which the electroactive species is in electronic communication with the negative electrode, the electroactive species is immobilized on the negative electrode. For example, the electroactive species may be part of a redox-active polymer immobilized on the electrode, in some cases by a composite layer (e.g., including a carbonaceous material, such as carbon nanotubes). In some embodiments in which the electroactive species is in electronic communication with the negative electrode, the electroactive species resides in a conductive medium in at least a portion of the electrochemical cell and is capable of undergoing electron transfer reactions with the electrode (directly or indirectly). For example, the electroactive species may be present (e.g., dissolved or suspended) in the conductive liquid of the electrochemical cell and may be able to diffuse sufficiently close to the negative electrode such that an electron transfer reaction can occur (e.g., to reduce the electroactive species to at least one reduced state) upon application of a potential difference across the electrochemical cell.

[0064] As mentioned above, in some embodiments, the first electroactive species is immobilized on the negative electrode. Such embodiments may be distinguished from other embodiments in which the electroactive species moves freely from one electrode to another, for example, by advection. A species immobilized on an electrode (e.g., a negative electrode) may be a species that cannot freely diffuse away or desorb from the electrode under a given set of conditions. The electroactive species can be immobilized on the electrode in various ways. For example, in some cases, the electroactive species can be immobilized on the electrode by binding to the surface of the electrode or to a species or substance bound to the electrode (e.g., by covalent bonding, ionic bonding, and / or intramolecular interactions, such as electrostatic forces, van der Waals forces, hydrogen bonding, etc.). In some embodiments, the electroactive species can be immobilized on the electrode by being adsorbed onto the electrode. In some cases, the electroactive species can be immobilized on the electrode by being polymerized onto the electrode. In certain cases, the electroactive species can be immobilized on the electrode by being included in a composition (e.g., a coating, a composite layer, etc.) applied or deposited on the electrode. In certain cases, electroactive species (e.g., polymeric or molecular electroactive materials) infiltrate a microfiber, or nanofiber, or carbon nanotube mat, such that the electroactive material is immobilized to the mat. The mat can provide enhanced surface area for electrolyte and gas access, as well as an extended network for electrical conductivity. In some embodiments, the electroactive species is part of a gel composition associated with the electrode (e.g., as a layer deposited on the electrode, as a composition that infiltrates the pores of the electrode, or as a composition that at least partially encapsulates components of the electrode, such as the fibers or nanotubes of the electrode).Gels (e.g., hydrogels, ionogels, organogels, etc.) containing such electroactive species can be prepared prior to association with the electrode (e.g., applied as a coating to form a layer), or the gel can be prepared in the presence of the electrode by contacting the electrode with a gel precursor (e.g., a prepolymer solution containing the electroactive species) (e.g., by coating or immersion), and then gel formation can be initiated (e.g., by crosslinking through the introduction of a crosslinking agent, a radical initiator, heating, and / or irradiation with electromagnetic radiation (e.g., ultraviolet radiation)).

[0065] In some embodiments, the electrochemical or electrochemical device further includes a positive electrode. In some, but not necessarily all, embodiments, the electrochemical cell includes a separator between the negative and positive electrodes. For example, with reference to FIG. 2, in some embodiments, the electrochemical cell 100 includes an optional separator 130 between the negative electrode 110 and the optional positive electrode 120. As used herein, the positive electrode of the electrochemical cell refers to the electrode from which electrons are removed during the charging process. For example, with reference again to FIG. 2, when the electrochemical cell 100 is charged (e.g., by application of a potential by an external power source), electrons pass from the positive electrode 120 to an external circuit (not shown). Thus, in some cases, species associated with the positive electrode, if present, can be oxidized to an oxidized state (a state with a reduced number of electrons) during the charging process of the electrochemical cell.

[0066] In some embodiments, the electroactive species in electronic communication with the negative electrode is a first electroactive species, and the positive electrode includes a second electroactive species. The second electroactive species may be of a different composition than the first electroactive species of the negative electrode, but in some embodiments, the second electroactive species is the same as the first electroactive species. In some embodiments, the positive electrode includes an electroactive layer (sometimes referred to as a complementary electroactive layer) including the second electroactive species. The complementary electroactive layer may be in the form of a composite and thus may be a complementary electroactive composite layer. In operation, this second electroactive species can serve as an electron source for the reduction of the first electroactive species present in the negative electrode. Similarly, the second electroactive species can serve as a sink for electrons during the oxidation of the first electroactive species. In this manner, the electroactive layer of the positive electrode can be described as "complementary." The second electroactive species can include, for example, a redox-active polymer. In some embodiments, the redox-active polymer is or includes a polymer that includes ferrocene (e.g., as a moiety attached to the polymer backbone). In some embodiments, the second electroactive species includes a metallocene (e.g., ferrocene). In some such cases, the second electroactive species includes a redox-active polymer that includes a metallocene. As a non-limiting embodiment, the redox-active polymer includes polyvinylferrocene. As another example, the second electroactive species can include a polymer that includes a thiophene. In some such cases, the second electroactive species includes poly(3-(4-fluorophenyl)thiophene). In some embodiments, the second electroactive species includes phenothiazine. As another example, in some embodiments, the second electroactive species includes (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (referred to as "TEMPO"), or a derivative thereof (e.g., including optional substituents). In certain cases, the second electroactive species comprises a faradaic redox species having a standard reduction potential at least 0.5 volts (V), at least 0.6 V, at least 0.8 V, and / or up to 1.0 V, up to 1.5 V, or more positive than the primary reduction potential of the first electroactive species.

[0067] In some embodiments, the second electroactive species comprises an intercalation compound. For example, the second electroactive species may comprise a metal ion intercalation compound. An exemplary class of intercalation compounds includes metal oxides. The intercalation compound may include an alkali metal ion, such as a lithium ion and / or a sodium ion intercalation compound. In some embodiments, the intercalation compound comprises an alkali metal ion transition metal oxide (e.g., lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and / or lithium oxide containing cobalt, manganese, and / or nickel). In some embodiments, the intercalation compound comprises an alkali metal transition metal polyoxyanion, such as a lithium transition metal phosphate. One example of a lithium transition metal phosphate suitable for the positive electrode is lithium iron phosphate (LiFePO4). In some embodiments, during a charge mode, oxidation of a second electroactive species in the form of an alkali metal ion intercalation compound (e.g., LiFePO4) drives the reduction of the first electroactive species, simultaneously providing a source of electrons for releasing alkali metal ions (e.g., lithium ions) that can be shuttled through the electrolyte (e.g., on or in a separator, if present) to the negative electrode to maintain charge balance and complete the electrochemical circuit. Conversely, during a discharge mode, reduction of the second electroactive species in the form of an alkali metal ion intercalation compound provides an acceptor for electrons from the oxidation of the first electroactive species, simultaneously allowing alkali metal ions (e.g., lithium ions) to be shuttled from the adjacent region of the negative electrode through the electrolyte (e.g., on or in a separator, if present) to the positive electrode where they can intercalate into the intercalation compound and maintain charge balance.

[0068] The complementary electroactive composite layer of the positive electrode can include an immobilized polymer composite of an electroactive species and another material (e.g., a carbonaceous material). Examples of carbonaceous materials include carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon black, Ketjen Black, carbon black Super P, or graphene. Other materials are possible. In certain cases, the second electroactive species can be immobilized on the positive electrode by being included in a composition (e.g., a coating, composite layer, etc.) applied or deposited on the positive electrode. In certain cases, the second electroactive species (e.g., a polymer or molecular electroactive material) infiltrates a microfiber, nanofiber, or carbon nanotube mat associated with the positive electrode, such that the second electroactive species is immobilized relative to the mat in the positive electrode. The second electroactive species can also be part of a gel associated with the positive electrode in the same or similar manner as described above for the first electroactive species.

[0069] According to one or more embodiments, the electroactive composite layer of the positive electrode can have a specific weight ratio of electroactive material to carbonaceous material. The weight ratio can be selected to facilitate a high current per mass of electroactive material. In some embodiments, the weight ratio of the mass of electroactive material to the mass of carbonaceous material for the complementary electroactive composite layer can be between 1:2 and 2:1. In some embodiments, the ratio can be 1:1. Other ratios are possible.

[0070] The separator can act as a protective layer that can prevent the electrochemical reactions at each electrode from interfering with each other. The separator can also electronically isolate the negative and positive electrodes from each other and / or from other components in the electrochemical cell, helping to prevent short circuits. In some embodiments, the electrochemical cell includes a conductive medium, and the separator contains at least a portion of the conductive medium (e.g., a conductive liquid). Those skilled in the art, given the benefit of this disclosure, will be able to select an appropriate separator. The separator can include a porous structure. In some cases, the separator is or includes a porous solid material. In some embodiments, the separator is or includes a membrane. The separator membrane can be made of a suitable material. For example, the separator membrane can be or include a plastic film. Non-limiting examples of included plastic films include polyamide, polyolefin resin, polyester resin, polyurethane resin, or acrylic resin containing dispersed lithium carbonate, potassium hydroxide, or sodium-potassium peroxide. Materials for the separator can include cellulose membranes, polymeric materials, or polymer-ceramic composites. Further examples of separators include polyvinylidene difluoride (PVDF) separators, PVDF-alumina separators, or Celgard.

[0071] In the context of the present disclosure, a conductive medium is understood to be a solid or fluid medium with sufficient ionic conductivity to support the operation of an electrochemical cell (e.g., by shuttling ions between the electrodes of the electrochemical cell to maintain charge balance). As previously mentioned, the conductive medium can be a liquid or solid electrolyte. In some embodiments, the conductive medium is or includes a non-volatile liquid. In some such cases, the conductive medium is or includes a room temperature ionic liquid, such as 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][TFN]). It should be understood that the conductive medium is capable of transporting ions but generally does not have electronic conductivity (e.g., metallic conductivity) that could short-circuit the electrochemical cell when brought into contact with the negative and positive electrodes.

[0072] In some cases, the separator contains a conductive liquid that acts as the conductive medium. In some embodiments, the separator is at least partially (or completely) impregnated with the conductive liquid. For example, the separator may absorb a certain amount of conductive liquid when immersed, coated, dipped, or otherwise associated with the conductive liquid. In some such cases where the separator is porous, some or all of the separator's pores (inside the separator and / or near its surface) may be at least partially filled with the conductive liquid. In some embodiments, the separator is saturated with the conductive liquid. A separator saturated with the conductive liquid generally refers to a separator containing the maximum amount of conductive liquid that can be contained in the volume of the separator at room temperature (23°C) and ambient pressure. In some embodiments, the electrochemical cell may be provided without any conductive liquid present in the separator, but the separator may contain a conductive liquid once it is in operation to perform a gas separation process. One way in which the separator may be able to contain the conductive liquid is by containing a material that has a relatively high porosity and / or can absorb and / or be wetted by the conductive liquid.

[0073] As mentioned above, in some embodiments, the conductive liquid comprises an ionic liquid, e.g., a room temperature ionic liquid ("RTIL"). RTIL electrolytes have low volatility (i.e., 10 -5 Less than Pa, e.g., 10 -10 ~10 -5 The electrode can have a room temperature vapor pressure of 0.2 Pa, thereby reducing the risk of drying out of the electrode and preventing significant evaporation or entrainment. In some embodiments, the ionic liquid comprises substantially all of the conductive liquid (e.g., at least 80% by volume, at least 90% by volume, at least 95% by volume, at least 98% by volume, at least 99% by volume, at least 99.9% by volume).

[0074] Ionic liquids can include an anion and a cation. Anions of ionic liquids include, but are not limited to, halides, sulfates, sulfonates, carbonates, bicarbonates, phosphates, nitrates, acetates, PF6 - , BF4 - , triflate, nonaflate, bis(triflyl)amide, trifluoroacetate ion, heptafluorobutanoate ion, ha Ionic liquid cations may include, but are not limited to, imidazolium, pyridinium, pyrrolidinium, phosphonium, ammonium, sulfonium, thiazolium, pyrazolium, piperidinium, triazolium, pyrazolium, oxazolium, guanadinium, and dialkylmorpholinium. In some embodiments, the room temperature ionic liquid comprises imidazolium as the cation component. As an example, in some embodiments, the room temperature ionic liquid comprises 1-butyl-3-methylimidazolium (“Bmim”) as the cation component. In some embodiments, the room temperature ionic liquid comprises bis(trifluoromethylsulfonyl)imide (“TFN”) as the anion component. In some embodiments, the room temperature ionic liquid comprises 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][TFN]).

[0075] In some embodiments, the room temperature ionic liquid comprises 1-butyl-3-methylimidazolium tetrafluoroborate (BF4) ([Bmim][BF4]).

[0076] In some embodiments, the conductive liquid comprises a low-volatility electrolyte solution. For example, the conductive liquid may comprise a liquid solvent having a relatively high boiling point and having dissolved ionic species (e.g., dissolved supporting electrolyte ions). The liquid solvent having a relatively high boiling point may be non-aqueous. For example, the liquid solvent may comprise N,N-dimethylformamide (DMF), etc.

[0077] In some cases, one or more electrodes of an electrochemical cell include an electroactive composite layer. For example, in some embodiments, the negative electrode includes an electroactive composite layer (e.g., a primary electroactive composite layer). Referring to FIG. 5 , the negative electrode 110 includes a composite electroactive composite layer 114 facing the positive electrode 120 of the electrochemical cell 500 according to certain embodiments. In certain cases, the positive electrode includes an electroactive composite layer (e.g., a complementary electroactive composite layer). For example, in FIG. 5 , the positive electrode 120 includes an electroactive composite layer 124 facing the negative electrode 110. The electroactive composite layer of the positive electrode may also be referred to as a complementary electroactive composite layer, since the electroactive species therein serve as an electron acceptor or electron source for the electroactive material of the negative electrode. In some cases, the electroactive composite layer of an electrode (e.g., negative electrode, positive electrode) spans the entire thickness dimension of the electrode. For example, the electroactive composite layer may intercalate throughout the thickness of the electrode. However, in some embodiments, the electroactive composite layer of the electrode does not extend through the entire thickness dimension of the electrode. In some such cases, the electroactive composite layer intercalates through a portion of the electrode's thickness, but not the entire thickness. In certain cases, the electroactive composite layer is a coating on the surface of another component of the electrode (e.g., a current collector, a gas permeable layer, etc.).

[0078] In some embodiments, the electroactive species of the electrodes (e.g., a first electroactive species of a negative electrode, a second electroactive species of a positive electrode) are part of an electroactive composite layer. For example, in FIG. 5, electroactive composite layer 114 includes a first electroactive species described herein, according to some embodiments. Similarly, in some embodiments, electroactive composite layer 124 includes a second electroactive species (e.g., polyvinylferrocene).

[0079] The negative electrode electroactive composite layer can also include a carbonaceous material in addition to the electroactive species. Examples of suitable materials include, but are not limited to, carbon nanotubes (e.g., single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon black, Ketjen Black, carbon black Super P, graphene, or combinations thereof. Other examples include immobilizing and / or coating electroactive species (e.g., in polymeric, molecular, or other form) in / on microfibers, nanofibers, or carbon nanotube mats by intercalation, grafting, chemical vapor deposition (CVD), or otherwise.

[0080] According to one or more embodiments, the electroactive composite layer of the negative electrode can have a specific weight ratio of electroactive species to carbonaceous material. The weight ratio can be selected to facilitate a high current per mass of electroactive material. In some embodiments, the weight ratio of the mass of electroactive material to the mass of carbonaceous material can be between 1:1 and 1:10. In some embodiments, the ratio can be 1:3. Other ratios are possible.

[0081] The negative electrode may further include a gas permeation layer. The gas permeation layer (which may also be referred to as a substrate layer) may be adjacent to the electroactive composite layer and face outward from the electrochemical cell. In some embodiments, the gas permeation layer is in contact with the first electroactive species. In some such cases, the gas permeation layer is in direct contact with the first electroactive species, and in other such cases, the gas permeation layer is in indirect contact with the first electroactive species. When a portion (e.g., a layer) is referred to as "on" or "in contact with" another portion, it should be understood that the portion can be directly on the other portion, or that an intervening portion (e.g., layer) may be present (in which case the portion is understood as "indirectly on" or "in indirect contact with" the other portion). A portion "directly on" or "in direct contact with" another portion means that no intervening portion is present. Also, when a portion is referred to as "on" or "in contact with" another portion, it should be understood that the portion can cover all or part of the other portion. In some embodiments, the gas permeable layer is in contact (eg, in direct contact or indirect contact) with the electroactive composite layer of the negative electrode.

[0082] The fluid mixture in the form of a gas stream (e.g., comprising a first Lewis acid gas and a second Lewis acid gas) can diffuse into the gas permeable layer and contact the electroactive composite layer. The gas permeable layer can include an electrically conductive solid material and act as a current collector in the cell.

[0083] The gas permeable layer may comprise a porous material. In some embodiments, the gas permeable layer has a porosity of, for example, 60% or more, 70% or more, 75% or more, 80% or more, or more. In some embodiments, the gas permeable layer has a porosity of 85% or less, 90% or less, or more. Combinations of these ranges are possible. For example, in some embodiments, the gas permeable layer of the negative electrode has a porosity of 60% or more and 90% or less. Other porosities are also possible. Examples of suitable materials for the gas permeable layer include, but are not limited to, carbon paper (treated, TEFLON®-treated, or untreated), carbon cloth, and nonwoven carbon mats. Other materials may also be used.

[0084] In some embodiments, the electrochemical cell includes a single negative electrode, while in other embodiments, the electrochemical cell includes more than one negative electrode. For example, in some embodiments, the negative electrode described herein is a first negative electrode, and the electrochemical cell includes a second negative electrode. A positive electrode can be present between the first negative electrode and the second negative electrode. The second negative electrode can also include a first electroactive species. The second negative electrode can be identical in construction and composition to the first negative electrode. In some embodiments, the electrochemical cell includes one or more negative electrodes, two or more negative electrodes, three or more negative electrodes, five or more negative electrodes, ten or more negative electrodes, and / or up to 15 negative electrodes, up to 20 negative electrodes, up to 50 negative electrodes, or more.

[0085] In some embodiments, the electrochemical cell includes a single separator (e.g., between the negative electrode and the positive electrode), while in other embodiments, the electrochemical cell includes more than one separator. For example, in some embodiments, the separator described herein is a first separator, and the electrochemical cell includes a second separator. In some embodiments in which a second negative electrode is present, the second separator can be present between the positive electrode and the second negative electrode. The second separator may be identical in construction and composition to the first separator. In certain cases, the second separator can include a conductive liquid (e.g., be saturated with a conductive liquid). In some embodiments, the electrochemical cell includes one or more separators, two or more separators, three or more separators, five or more separators, ten or more separators, and / or up to 15 separators, up to 20 separators, up to 50 separators, or more. In some cases, each of the separators is present between the respective negative and positive electrodes.

[0086] In some embodiments of electrochemical cells in which a positive electrode has negative electrodes on either side (e.g., a first negative electrode and a second negative electrode), the positive electrode includes a second electroactive species facing each of the negative electrodes. In some such embodiments, the positive electrode includes two complementary electroactive composite layers, each facing one of the negative electrodes.

[0087] The positive electrode may further include a substrate layer disposed adjacent to or between one or more electroactive composite layers. The substrate layer may be in direct or indirect contact with one or more electroactive composite layers. The substrate layer of the positive electrode may comprise the same or a different material as the substrate layer of the negative electrode (if present). For example, the substrate layer may comprise a material such as carbon paper (treated, TEFLON®-treated, or untreated), carbon cloth, or a nonwoven carbon mat. In some embodiments, the substrate may comprise, for example, a mat including carbon nanotubes, microfibers, nanofibers, or a combination thereof. Other materials are also possible. The substrate layer of the positive electrode may comprise a conductive material and act as a current collector in the cell. In some embodiments, the substrate comprises a metal and / or a metal alloy. For example, the substrate may include a metal and / or metal alloy foil (e.g., having a relatively small thickness of 200 microns or less, 100 microns or less, 10 microns or less, and / or only 1 micron or less). Examples of suitable foils may include, but are not limited to, aluminum foil and titanium foil. As a specific example, in some embodiments, a positive electrode includes a substrate between a first complementary electroactive composite layer facing a first negative electrode and a second complementary electroactive composite layer facing a second negative electrode. In this situation, the electroactive composite layer of a positive electrode can face a particular electrode (e.g., a negative electrode) if a line extending from a majority of the electroactive composite layer can intersect that electrode without passing through the substrate. An object (e.g., an electroactive composite layer) can face another object if it contacts the other object or if one or more intermediate materials are disposed between the surface and the other object. For example, two objects facing each other can be in contact or can include one or more intermediate materials (eg, separators) between them.

[0088] 6 shows a schematic cross-sectional view of an example electrochemical cell having one or more of the aforementioned components, according to some, but not necessarily all, embodiments. The electrochemical cell 600 includes a positive electrode 120 between two negative electrodes 110. A separator 130 separates the positive and negative electrodes 120 and 110. Each of the negative electrodes 110 includes an optional gas permeable layer 112 disposed away from the center of the cell 100 and an optional primary electroactive composite layer 114 facing the positive electrode 120. In some embodiments, the positive electrode 120 includes a substrate layer 122 and two complementary electroactive composite layers 124 thereon. For example, the various components of the electrochemical cell 100, including the aforementioned electrode materials (e.g., electroactive species), can have certain properties described throughout this disclosure. For example, the configuration of two outwardly facing negative electrodes 110 shown in FIG. 2 may, in some cases, provide the advantage of doubling the gas adsorption area exposed to the gas compared to an electrochemical cell including a single negative electrode and a single positive electrode. The electrochemical device may be provided in any of a variety of forms, depending on the desired application and / or properties of the fluid mixture. The electrochemical device may be configured to electrochemically capture and / or separate Lewis acid gases from the gas mixture. In some such cases, the electrochemical device includes a chamber having a gas or vacuum headspace that can be at least partially filled with the gas fluid mixture. In some such embodiments, the fluid inlet of the chamber is fluidly connected to a source of the gas mixture and one or more components for transporting the gas mixture, such as a pump or vacuum valve and associated valves.

[0089] In some embodiments, the electrochemical device is configured to electrochemically capture and / or separate the Lewis acid gas from the liquid mixture. In some such cases, the electrochemical device includes a chamber that can be at least partially filled with a solution. In certain cases, the electrochemical device, including the chamber and electrochemical cell, is configured similarly to a redox flow battery, in which one of the flowing liquid solutions enters through the fluid inlet of the chamber and exits through the fluid outlet during operation. In certain embodiments, the portion of the chamber that is in fluid contact with the negative electrode is fluidly connected to an absorbent material. As a non-limiting example, the chamber can be fluidly connected to an absorber tower. However, in some embodiments, the electrochemical device is configured so that the first Lewis acid gas is directly captured at the negative electrode (e.g., by combining with the electroactive species during and / or after application of a potential difference).

[0090] In some embodiments, the electrochemical cell is configured as a solid-state electrochemical cell system. In some such cases, the electroactive species may be immobilized on at least a portion of the negative electrode, as described above.

[0091] The electrochemical device can be configured as a gas separation system. According to one or more embodiments, one or more electrochemical cells described herein (e.g., configured to selectively remove Lewis acid gases) can be incorporated into a gas separation system. The gas separation system can include multiple electrochemical cells in fluid communication with a gas inlet and a gas outlet according to any of the embodiments described herein. The electrochemical cells are electrically connected in parallel or in series, as described in more detail below.

[0092] The gas separation system may include an external circuit connecting the negative electrode (or first and second negative electrodes, if both are present) and positive electrode of each electrochemical cell to a power source configured to apply a potential difference across the negative electrode(s) and positive electrode of each electrochemical cell.

[0093] FIG. 7A shows a schematic diagram of an exemplary system for performing a gas separation process during a charging mode, according to one or more embodiments. In FIG. 7A, a potential difference is applied across each of the electrochemical cells 700, each operating in a charging mode, according to certain embodiments. In the charging mode, a redox reaction (e.g., reduction) of a first electroactive species at the anode 710 increases the affinity between the electroactive species and a Lewis acid gas 790, according to certain embodiments. A gas mixture 775 including the Lewis acid gas 790 is introduced into the system and passed in proximity to the anode 710. The increased affinity causes the Lewis acid gas (e.g., SO) to bind to the electroactive material, according to certain embodiments. In this manner, at least a portion of the Lewis acid gas is separated from the gas mixture 775 to produce a treated gas mixture 785.

[0094] In some embodiments, a gas separation system includes a plurality of electrochemical cells, and a flow field exists between at least a portion (e.g., some or all) of the plurality of electrochemical cells. By way of example, FIG. 7B shows a schematic diagram of an exemplary system including a flow field 711 separating electrochemical cells 570 that performs a gas separation process during a charging mode, according to one or more embodiments. It should be understood that when a first object is present between a second object and a third object, it can be between the entire first object and the entire second object, or between a portion of the first object and a portion of the second object. In some embodiments, the flow field between two adjacent electrochemical cells is directly adjacent to each of the adjacent electrochemical cells, such that there are no intervening structures / layers between the flow field and the electrochemical cells. However, in some embodiments, the flow field between two adjacent electrochemical cells is indirectly adjacent to one or two cells, such that there are one or more intervening structures / layers, such as conductive solids.

[0095] A flow field generally refers to a solid structure configured to define a path through which a fluid can flow. In some cases, a flow field includes a solid article that defines pores or channels for fluid flow while allowing the fluid to be exposed to adjacent structures. Suitable materials for the solid article in a flow field include, but are not limited to, polymeric materials (e.g., plastics), metals / metal alloys, graphite, and composite materials (e.g., graphite-polymer composites). In some embodiments, a flow field includes a solid article that includes one or more surfaces with patterned channels. The channel pattern can be selected to effectively distribute the fluid (e.g., gas) across one or more dimensions of the flow field. Suitable channel patterns include, but are not limited to, serpentine, parallel, and interdigitated. 7C, 7D, and 7E show schematic side views of a flow field with a serpentine pattern 711a, a flow field with a parallel pattern 711b, and a flow field with an interdigitated pattern 711c, each with fluid flow direction shown as arrows according to certain embodiments. The flow field channel patterns can be formed by, for example, etching, cutting, stamping, molding, milling, or additive manufacturing. In some embodiments, the flow field comprises a porous solid. For example, the flow field can comprise carbon fiber paper, felt or cloth, or metal foam.

[0096] 7B, Lewis acid gas 790 from fluid mixture 775 is distributed along the facial area of ​​electrode 710 via flow field 711 (e.g., via channels not shown). In the context of the present disclosure, it has been found that the flow field can help distribute the gas mixture relatively uniformly across the electrode and can help regulate the duration of gas exposure to the electrode (e.g., to promote efficient capture of the target gas). A relatively uniform gas distribution can increase efficiency by utilizing a greater percentage of the electrode area (e.g., containing at least one reduced-state electroactive species) for binding the target gas. In some embodiments, during at least a portion of the charging process, the flux of the gas mixture across at least 25%, at least 50%, at least 75%, at least 90%, at least 95%, or more of the face area of ​​the negative electrode of the system is within 50%, within 25%, within 15%, within 10%, within 5%, within 2%, within 1%, or less of the average flux across the entire face area of ​​the negative electrode during the charging process.

[0097] As described above, a gas separation system can include multiple electrochemical cells electrically connected in parallel or in series. Those skilled in the art with the benefit of this disclosure will generally understand how to electrically connect electrochemical cells to form a circuit. Such connection can be achieved by establishing a conductive path for electron flow between the electrodes of the electrochemical cells (i.e., establishing electrical coupling between the electrodes). In some cases, the conductive path can be established by one or more conductive solid materials (e.g., conductive metals, alloys, polymers, composites, carbonaceous materials, or combinations thereof). For example, the conductive path can be established by wiring the electrodes of the electrochemical cells. The electrochemical cells can have any of the configurations described above. For example, in some embodiments, some or all of the electrochemical cells of the system have a single negative electrode (e.g., containing a first electroactive species), a single positive electrode (e.g., containing a second electroactive species), and, optionally, a separator between the first and second positive electrodes. 8A shows a schematic diagram of an arrangement of electrochemical cells 1100 in one such system 1000, where each electrochemical cell 1100, in turn, includes an anode 1010, an optional separator 1020, and a cathode 1030, according to one particular embodiment. A gas mixture 1075 including a target gas can be introduced into the system such that the gas mixture 1075 passes adjacent to the anode 1010 of a first electrochemical cell 110 and the cathode 1030 of an adjacent second electrochemical cell 1100. While FIG. 8A shows three electrochemical cells 1100, it should be understood that any of a variety of suitable numbers of electrochemical cells can be used in a gas separation system (e.g., electrically connected in parallel or series) as needed depending on the requirements of a particular application.

[0098] In other embodiments, some or all of the electrochemical cells of the gas separation system include a positive electrode (e.g., including a second electroactive species), a first negative electrode (e.g., including a first electroactive species), a second negative electrode (e.g., including a first electroactive species), a first separator between the first negative electrode and the positive electrode, and a second separator between the positive electrode and the second negative electrode. Examples of such electrochemical cells are shown in Figures 6 and 7A-7B.

[0099] 8B shows a schematic diagram of a configuration in which multiple electrochemical cells 1100 of system 1000 are electrically connected in parallel, according to certain embodiments. In the parallel configuration, each negative electrode 1010 is electrically coupled to a first terminal (e.g., of a power source) and each positive electrode 1030 is electrically coupled to a second terminal (e.g., of a power source). For example, in FIG. 8B, each negative electrode 1010 is electrically coupled to a first terminal of the power source via wire 115, and each positive electrode 1030 is electrically coupled to a second terminal of the power source via wire 116, according to certain embodiments.

[0100] 8C shows a schematic diagram of a configuration in which multiple electrochemical cells 11000 of system 1000 are electrically connected in series, according to certain embodiments. In the series configuration, the positive electrode of a first electrochemical cell is electrically connected to the negative electrode of a second electrochemical cell in the system. For example, in FIG. 8B, the negative electrode 1010 of a first electrochemical cell 1100a is electrically connected to the positive electrode 1030 of a second electrochemical cell 1100b via wire 1017, and the negative electrode 1010 of the second electrochemical cell 1100b is electrically connected to the positive electrode 1030 of a third electrochemical cell 1100c via wire 1018, according to certain embodiments. Furthermore, according to certain embodiments, the positive electrode 1030 of the first electrochemical cell 1100a is electrically coupled to a first terminal of the power source via wire 114, and the negative electrode 1030 of the third electrochemical cell 1100a is electrically coupled to a second terminal of the power source via wire 119.

[0101] In the context of the present disclosure, it has been determined that certain configurations of a gas separation system including multiple electrochemical cells electrically connected in series can promote relatively efficient charge transport and / or gas transport. For example, in some embodiments, conductive materials between the electrochemical cells can establish a conductive path other than using external wiring. For example, a gas separation system can include a first electrochemical cell and a second electrochemical cell electrically connected in series, where an electrical connection is established through one or more conductive materials between the first and second electrochemical cells. For example, any of a variety of suitable conductive materials can be disposed between the electrochemical cells to establish an electrical connection between the negative electrode of the first electrochemical cell and the positive electrode of the second electrochemical cell. For example, the conductive material can be a conductive solid. The conductive solid can include, for example, a metal and / or metal alloy (e.g., steel, silver metal / alloy, copper metal / alloy, aluminum metal / alloy, titanium metal / alloy, nickel metal / alloy). In some embodiments, the conductive solid is a carbonaceous material (e.g., graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, carbon mat (e.g., carbon nanotube mat), KetjenBlack, carbon black Super In some embodiments, the conductive solid comprises a composite of a conductive solid and a binder resin. In some embodiments, the conductive solid between the electrochemical cells comprises a conductive polymer material.

[0102] In some, but not necessarily all, embodiments, the conductive material between the electrochemical cells comprises a bipolar plate. It should be understood that, in the context of the present disclosure, the plate need not necessarily be flat. Bipolar plates are known to those skilled in the art and are typically used in fields other than gas separation, such as in fuel cells. The bipolar plate may be configured to separate a fluid (e.g., gas) in contact with the positive electrode from a fluid in contact with the negative electrode. The bipolar plate may comprise a conductive solid, such as steel, titanium, or graphite.

[0103] In some embodiments, at least a portion of the multiple electrochemical cells (e.g., connected in series) are separated by a flow field. As previously discussed, locating a flow field between adjacent electrochemical cells can promote beneficial gas distribution and relatively efficient interaction (e.g., for bonding) between the gas and the electrodes. In some embodiments, the bipolar plates described above include flow fields (e.g., by etching fluid pathways on one or both sides of the plate), while in other embodiments, different flow fields are used instead of or in addition to bipolar plates containing flow fields.

[0104] FIG. 9 shows a schematic diagram of an exemplary gas separation system 1000 including electrochemical cells 1100 electrically connected in series via one or more conductive materials between the cells, according to certain embodiments. In FIG. 9, the system 1000 includes conductive solid material in the form of bipolar plates 1012 and ribs 1014. The ribs of the gas separation system may be made from any of the conductive solid materials described above. In the embodiment shown in FIG. 9, a first electrochemical cell 1100a is separated from a second electrochemical cell 1100b via the bipolar plates 1012 and ribs 1014. The bipolar plates 1012 and ribs 1014 may be directly adjacent to the negative electrode 1010 of the first electrochemical cell 1100a and the positive electrode 1030 of the second electrochemical cell 1100b, thereby establishing a conductive path for the series connection. Other electrochemical cells in the system may be electrically connected in a similar manner. While FIG. 9 illustrates bipolar plates and ribs, such illustration is non-limiting and other configurations are possible (e.g., no bipolar plates, no ribs, etc.). FIG. 9 also illustrates flow fields 1011, as needed, to separate the electrochemical cells 1100, according to certain embodiments. In some embodiments, one or more components (e.g., conductive solids, e.g., ribs) can establish channels between the negative and positive electrodes of adjacent electrochemical cells. For example, the ribs 1014 in FIG. 9 can have dimensions such that the channels 1013 establish a path for a gas (e.g., a gas mixture) to flow between the electrochemical cells 1011 and interact with the electrodes. For example, a gas mixture 1075 can pass between the first electrochemical cell 1100a and the second electrochemical cell 1100b via the channels 1013 and through the flow fields 1011, according to certain embodiments.

[0105] The flow of current in certain of the aforementioned embodiments encounters less electrical resistance than in other configurations. For example, in some embodiments where electrochemical cells are connected in series through conductive material between at least a portion of a stack of electrochemical cells, current can flow in a direction perpendicular to the stack. FIG. 9 illustrates such an example, where current can flow in a direction x perpendicular to the electrochemical cells 1100, while the gas mixture 1075 can flow in a direction parallel to the electrochemical cells 1100. In FIG. 9, the path along which the current travels is relatively short and determined by the thickness of the bipolar plates 1012 and ribs 1014. In some embodiments, the thickness of one or more conductive solids between the electrochemical cells is 10 mm or less, 5 mm or less, 2 mm or less, 1 mm or less, and / or no more than 0.5 mm, no more than 0.2 mm, no more than 0.1 mm, or even less. In contrast, in embodiments in which electrochemical cells are electrically connected in parallel or electrically connected in series via external wiring, current must flow up to the entire height and / or length of the electrodes (e.g., the electrode current collectors) and through the electrode tabs to reach the external wiring. Such height and / or length may be, for example, at least 1 cm, at least 2 cm, at least 5 cm, at least 10 cm, and / or up to 20 cm, up to 50 cm, up to 100 cm, or more. In such embodiments, the greater the distance that current must travel, generally the greater the overall resistance of the cell, which may reduce the charge transport and / or energy efficiency of the methods for separating at least some gases described herein.

[0106] In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) can absorb gas (e.g., SO2, CO2) at a particular rate. For example, in some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) can absorb gas (e.g., SO2, CO2) at a particular rate. 2At least 0.0001 mol per second, 1 m 2 At least 0.0002 mol per second, 1 m 2 In some embodiments, the negative electrode or a portion thereof (e.g., the electroactive composite layer of the negative electrode, if present) has an absorption capacity rate of at least 0.0005 mol per second, or greater. 2 0.001 mol or less per second, 1 m 2 0.0008 mol or less per second, 1 m per second 2 In some embodiments, the electroactive composite layer has an absorption capacity rate of 1 m per second or less. 2 At least 0.0001 per second and 1 m per second 2 The absorbency rate is 0.0005 mol / L or less. Other absorbency rates are possible.

[0107] In some embodiments, the electroactive composite layer of the negative electrode can be exposed to a fluid mixture (e.g., a gas mixture), e.g., up to 5 cm 2 or larger, 8cm 2 or larger, 10cm 2 or larger and / or 10 cm 2 Up to 20cm 2 Up to 50cm 2 Up to 1m 2 The specific surface area may be up to or greater than 1000 nm. Other values ​​are possible.

[0108] In some embodiments, at least some or all of the electrodes (e.g., negative electrodes, positive electrodes) described herein comprise a porous material. The porous electrodes can be made from any suitable material and / or can be configured in any suitable shape or size. In a non-limiting embodiment, the electrodes comprise a porous carbonaceous material. The term carbonaceous material has its ordinary meaning in the art and refers to a material comprising carbon or graphite that is electrically conductive. Non-limiting examples of carbonaceous materials include carbon nanotubes, carbon fibers (e.g., carbon nanofibers), carbon mats (e.g., carbon nanotube mats), and / or graphite. In some such embodiments, the electrodes may be made partially from a carbonaceous material, or the carbonaceous material may be deposited over an underlying material. The underlying material generally comprises an electrically conductive material, such as a metal and / or metal alloy solid (e.g., steel, copper, aluminum, etc.). Other non-limiting examples of electrically conductive materials are described herein.

[0109] In some embodiments, the electrodes (e.g., negative electrode, positive electrode) are porous. The porosity of an electrode can be measured as the percentage or fraction of void space in the electrode. The percent porosity of an electrode can be measured using techniques known to those skilled in the art, such as the volume / density method, the water saturation method, the water evaporation method, mercury intrusion porosimetry, and nitrogen gas adsorption. In some embodiments, the electrode is at least 10% porous, at least 20% porous, at least 30% porous, at least 40% porous, at least 50% porous, at least 60% porous, at least 70% porous, or more. In some embodiments, the electrode is up to 90% porous, up to 85% porous, up to 80% porous, up to 70% porous, up to 50% porous, up to 30% porous, up to 20% porous, up to 10% porous, or less. Combinations of these ranges are possible. For example, the electrode can be at least 10% porous and up to 90% porous. The pores may be open pores (e.g., with at least some of the open pores and / or other pores at the outer surface of the electrode). In some cases, only a portion of the electrode is porous. For example, in some cases, only a single surface of the electrode is porous. As another example, in some cases, the outer surface of the electrode is porous and the inner core of the electrode is substantially non-porous (e.g., 20% or less porous, 10% or less porous, 5% or less porous, 1% or less, or less). In certain embodiments, the entire electrode is substantially porous.

[0110] In some embodiments, the electrochemical cell has a specific cycle time. The cycle time of an electrochemical cell generally refers to the time it takes to perform one charge mode and one discharge mode. The cycle time may be at least 60 seconds, at least 100 seconds, at least 300 seconds, at least 500 seconds, at least 1000 seconds, or longer. In some embodiments, the cycle time is 3600 seconds or less, 2400 seconds or less, 1800 seconds or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the cycle time is at least 60 seconds and 3600 seconds or less, or at least 300 seconds and 1800 seconds or less.

[0111] According to some embodiments, the electrochemical cell and its components have a particular thickness depending on the desired application (e.g., ventilation system air gas separation, direct air capture, etc.). In some embodiments, the electrochemical cell has a thickness of at least 10 μm, at least 20 μm, at least 50 μm, at least 100 μm, at least 200 μm, at least 300 μm, at least 500 μm, or more. In some embodiments, the electrochemical cell has a thickness of 750 μm or less, 600 μm or less, 500 μm or less, 300 μm or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the electrochemical cell has a thickness of at least 200 μm and 750 μm or less. In some embodiments, the electrochemical cell has a thickness of at least 10 μm and 750 μm or less.

[0112] In some embodiments, the negative electrode or positive electrode has a thickness of at least 0.5 μm, at least 1 μm, at least 2 μm, at least 5 μm, at least 10 μm, at least 20 μm, at least 50 μm, at least 75 μm, at least 100 μm, or more. In some embodiments, the negative electrode or positive electrode has a thickness of 200 μm or less, 150 μm or less, 100 μm or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the negative electrode or positive electrode has a thickness of at least 50 μm and 200 μm or less. In some embodiments, the negative electrode or positive electrode has a thickness of at least 0.5 μm and 200 μm or less.

[0113] In some embodiments, the negative or positive electrode electroactive composite layer has a thickness of at least 10 nm, at least 20 nm, at least 40 nm, at least 0.1 μm, at least 0.2 μm, at least 0.5 μm, at least 1 μm, at least 2 μm, at least 5 μm, at least 10 μm, at least 50 μm, at least 100 μm, or more. In some embodiments, the negative or positive electrode electroactive composite layer has a thickness of 200 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, 2 μm or less, 1 μm or less, 0.5 μm or less, 0.2 μm or less, 0.1 μm or less, or less. Combinations of these ranges are possible. For example, in some embodiments, the negative or positive electrode electroactive composite layer has a thickness of 10 μm or more and 200 μm or less, hi some embodiments, the negative or positive electrode electroactive composite layer has a thickness of 10 nm or more and 100 nm or less, or 50 nm or more and 500 nm or less.

[0114] The various components of the system, such as electrodes (e.g., anode, cathode), power source, electrolyte, separator, container, electrical circuitry, insulating materials, etc., can be fabricated by one skilled in the art from any of a variety of components. The components can be molded and machined in either a green or fired state. They may be processed, extruded, pressed, isopressed, infiltrated, coated, or formed by any other suitable technique. Those skilled in the art will readily recognize techniques for forming the components of the systems herein.

[0115] The electrodes (e.g., negative electrodes, positive electrodes) described herein can be of any suitable size or shape. Non-limiting examples of shapes include sheets, cubes, cylinders, hollow tubes, spheres, etc. The electrodes can be of any suitable size depending on the application for which they are used (e.g., gas separation from ventilated air, direct air capture, etc.). In addition, the electrodes can include means for connecting the electrode to another electrode, a power source, and / or another electrical device.

[0116] Various electrical components of the system can be in electrical communication with at least one other electrical component by a means for connection. The means for connection can be any material that allows electrical flow to occur between a first component and a second component. A non-limiting example of a means for connecting two electrical components is wiring comprising a conductive material (e.g., copper, silver, etc.). In some cases, the system can also include electrical connectors between two or more components (e.g., wiring and electrodes). In some cases, the wiring, electrical connectors, or other means for connection can be selected to have a low material resistance. In some cases, the resistance can be substantially lower than the resistance of the electrodes, electrolyte, and / or other components of the system.

[0117] In some embodiments, the methods and electrochemical devices described herein can be implemented and configured as one or more of the systems described in U.S. Patent Application No. 2017 / 0113182, published April 27, 2017, entitled "Electrochemical Process for Gas Separation," filed October 26, 2016 as Application No. 15 / 335,258, which is incorporated herein by reference in its entirety for all purposes.

[0118] U.S. Provisional Application No. 62 / 892,975, filed August 28, 2019, entitled "Electrochemically Mediated Acid Gas Removal and Concentration," and U.S. Provisional Application No. 62 / 988,851, filed March 12, 2020, entitled "Electrochemical Capture of Lewis Acid Gases," are each incorporated herein by reference in their entirety for all purposes.

[0119] The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention. [Example]

[0120] Example 1 This example describes the reactivity of various electroactive species with Lewis acid gases as studied by cyclic voltammetry.

[0121] Figure 10A shows the cyclic voltammetry of 1,4-naphthoquinone (p-NQ) in dry N,N-dimethylformamide solution containing 0.1 M tetra-n-butylammonium hexafluorophosphate ([nBu4][PF6]) saturated with either N2, CO2, or SO2. The cyclic voltammograms were acquired at a scan rate of 100 mV / s. The cyclic voltammetry in Figure 10A exhibited the expected behavior under N2 and CO2, where the secondary (more negative) reduction wave shifted positively under CO2 relative to N2, while the primary reduction wave did not. However, in the presence of SO2, the primary (less negative) reduction wave shifted positively along with the secondary reduction wave. This indicated strong association of the semiquinone with the strong Lewis acid SO2, which caused a large shift in the Nernst potential. The desorption-oxidation peak of the complex of reduced 1,4-naphthoquinone and SO2 appeared at potentials more positive than that of the CO2 complex, further confirming the strong association of SO2 with the semiquinone and quinone dianions. The difference in cyclic voltammograms indicated different association strengths between reduced 1,4-naphthoquinone and SO2 and CO2.

[0122] These cyclic voltammetry results demonstrated that certain electroactive species, such as 1,4-naphthoquinone, react strongly with both SO2 and CO2, resulting in limited binding without selectivity upon exposure to a mixture of both Lewis acid gases. This lack of selectivity can be problematic in certain applications, such as electrochemical flow systems for carbon dioxide capture, where the gas mixture contains both CO2 and SO2 and SO2, thus potentially reducing the CO2 capture efficiency. The difference in the association strengths of 1,4-naphthoquinone with CO2 and SO2 suggests that quinone "poisoning" is quite possible in flow systems for carbon capture from industrial exhaust gases, where sulfur oxides are present at concentrations of 1,000–10,000 ppm. This is likely due primarily to differences in oxidation potentials, where an electrochemical cell operating at a potential difference roughly equivalent to the difference between the reduction of the quinone and the oxidation of its complex with CO2 could not provide sufficient energy to desorb the quinone-SO2 complex. This leads to a buildup of compounds and subsequently to a decrease in the system's capacity for CO2.

[0123] It has been found that this lack of selectivity can be overcome by introducing an electrochemical desulfurization step that removes sulfur oxides from the gas mixture (e.g., flue gas) prior to the electrochemical carbon capture step. Such an electrochemical desulfurization step can involve determining electroactive species and / or conditions to selectively capture sulfur dioxide (or other Lewis acid gases) while allowing negligible carbon dioxide capture. Toward that end, it has further been found that similar flow systems can be designed using electroactive species (e.g., quinones) that, upon reduction, have a lower potential density on oxygen, resulting in a relatively weaker base than 1,4-naphthoquinone.

[0124] This is achieved with 2,3-dicyano-1,4-naphthoquinone (DCNQ). Figure 10B shows the cyclic voltammetry of DCNQ in dry N,N-dimethylformamide solution containing 0.1 M [nBu4][PF6] saturated with either N2, CO2, or SO2. The cyclic voltammograms were acquired at a scan rate of 100 mV / s. The cyclic voltammetry in Figure 10B shows its behavior under CO2 as similar to that under N2, where only the dianion (formed during the secondary reduction) reacted weakly with CO2. This weak interaction was demonstrated by the slight positive shift of the secondary reduction wave and the appearance of a very small oxidative desorption peak. Nevertheless, one conclusion supported by the positive shift of the two reduction waves in Figure 10B and the appearance of the significantly positively shifted desorption-oxidative peak is that the interaction of DCNQ with SO2 was very strong. These results demonstrate that certain electroactive species (e.g., with certain substituents) have reduced states in which they can react with a first Lewis acid gas (e.g., SO2), but in which reaction with a second Lewis acid gas (e.g., CO2) is thermodynamically unfavorable.

[0125] Example 2 This example describes the reaction of various electroactive species with Lewis acids in ionic liquids (ILs).

[0126] The reactions of DCNQ and p-NQ with SO2 were studied by thermogravimetric analysis (TGA). DCNQ was reduced using two equivalents of cobaltocene to give DCNQ in [bmim][TF2N]. 2- A 0.3 M solution of the dianion was obtained. This was dissolved in 30 mL of 1% SO2 and the remaining N2. -1 p-NQ in TGA using a flow of 2- Dianions and NQs ·- It was used with a semiquinone ionic liquid (IL) solution. Figure 11A shows the DCNQ under 1% SO2. 2- , NQ ·- and NQ 2- Figure 11B shows the TGA analysis of DCNQ in N2.2- , NQ ·- and NQ 2- 11A and 11B show the TGA analysis of NQ 2- and DCNQ 2- It was found that both reacted effectively stoichiometrically with SO2 to form stable diadducts, which were not released under pure N2 flow. ·- The ability of is NQ as expected. 2- Although it was smaller than NQ ·- pK a But low pK a DCNQ high enough to react with strong Lewis acids such as SO2 2- pK a Since the HCl-containing HCl solution is similar to that of the HCl-containing HCl solution, it did not release SO2 at the same rate as it released CO2 under pure N2. This resulted in the release of the stronger Lewis base NQ2, as can be seen in Figures 11C and 11D. 2- Upon sulfonation of NQ, stronger bonds were formed, which allowed a constant capacity for SO2 to be maintained at high temperatures (up to 150 °C), and no SO2 was released under pure N2 flow. Figure 11C shows the NQ at different temperatures. 2- Figure 11D shows the TGA measurements of SO2 uptake by NQ at different temperatures. 2- The TGA measurements of SO2 release by DCNQ are shown. 2- The lower basicity of DCNQ resulted in weaker sulfonation, which in turn resulted in a smaller capacity for SO at higher temperatures. Figure 11E shows the results of the analysis of DCNQ at different temperatures. 2- Figure 11F shows TGA measurements of SO2 uptake by DCNQ at different temperatures. 2- 1 shows TGA measurements of SO2 release by

[0127] DCNQ 2- and NQ 2- Relative pK of aThis at least partially explains their reactivity with CO2 and SO2 and is believed to be the result of electron density modulation on the nucleophilic oxygen (phenoxide) moiety that arises during the primary and secondary reduction of quinones. Thus, electroactive species, such as quinones with finely tuned electron densities, can be used to selectively react with a variety of electrophiles at different Lewis base strengths in custom electrochemical systems capable of performing sequential separations.

[0128] In addition to modulating the electron density on the quinone molecule, which directly affects the thermodynamics of the electrochemical reaction, it has been found that in the context of this disclosure it is possible to impart additional selectivity to the resulting nucleophile through steric hindrance or affinity. This could be done by attaching various groups around the nucleophilic center to accommodate the reductive addition of one target over another.

[0129] Figure 12A shows TGA measurements of CO2 capture using reduced DCNQ at 30°C under 100% CO2. Figure 12B shows TGA measurements showing that CO2 is released when the reactants are removed. Thus, reduced DCNQ reacts reversibly with CO2 but irreversibly with SO2.

[0130] Example 3 This example describes a computational analysis of DCNQ to gain insight into its electronic structure and thermodynamic properties as they relate to its reactivity with Lewis acid gases.

[0131] Calculations of the neutral, singly reduced (semiquinone), and doubly reduced (dianion) states of DCNQ were performed using density functional theory. All electronic structure calculations were performed in Q-Chem® version 5.1.1. The equilibrium structures are from B3LYP-D3(op) / 6-31++ of theory in Witte J, Mardirossian N, Neaton JB, Head-Gordon M. Assessing DFT-D3 Damping Functions Across Widely Used Density Functionals: Can We Do Better? Journal of Chemical Theory and Computation. 2017; 13(5):2043-2052, which is incorporated herein by reference in its entirety for all purposes. G ** The 1,4-naphthoquinone was determined at the 1,4-naphthoquinone level using spin-unrestricted wave functions, Grimme dispersion corrections, and optimized power approach corrections. Naphothoquinone (Q) is treated as a neutral singlet and its semiquinone anion is (Q-) and the CO2 adduct anion were treated as the -1 doublet (QCO2-) and the dianion Q 2- , single adduct Q(CO2) 2- and the diadduct Q(CO2)2 2- Geometry optimizations in the gas phase and in a solvated environment (using the SMD solvent SCRF) were performed on structures constructed using the Avogadro® computer program after optimization using the MMFF94 force field. A systematic rotor search was performed to identify QCO2 - , QCO2 2- and Q(CO2)2 2- A low lying conformer of was identified.

[0132] The ground-state binding energy, including the zero-point energy (ZPE) and thermal and solvation contributions, was calculated by subtracting the overall electronic energy of the optimized isolated species from the optimized complex. Basis set superposition error (BSSE) was accounted for by a counterpoise scheme. Frequency analysis was used to confirm that the ground-state structure was a minimum on the potential energy surface.

[0133] Natural bond orbital (NBO) partial charges and orbital characteristics were obtained using the NBO v6.0 package interfaced with Q-Chem®, and second-generation ALMO-EDA was performed within Q-Chem®. Reduction potentials were determined by the procedure suggested by Isse AA, Gennaro A. Absolute Potential of the Standard Hydrogen Electrode and the Problem of Interconversion of Potentials in Different Solvents. Journal of Physical Chemistry B. 2010; 114(23):7894-7899, which is incorporated herein by reference in its entirety for all purposes. For reduction potential calculations, To this end, the structure was optimized in the solvent SCRF (using parameters for N,N-dimethylformamide), the electronic free energy was determined by Fermi-Dirac statistics at 4.28 V obtained as an absolute value for the standard hydrogen electrode, and the liquid junction potential was adjusted using data from Diggle JW, Parker AJ. Liquid junction potentials in electrochemical cells involving a dissimilar solvent junction. 1974 pp. 1617-1621, which is incorporated herein by reference in its entirety for all purposes.

[0134] 13A-13C show the calculated geometric change of DCNQ upon reduction. The standard reduction potential for the reduction of DCNQ was calculated under standard conditions as follows:

number

[0135] Electrostatic potential (ESP) maps were also calculated for various reduction states of DCNQ and 1,4-naphthoquinone. Figure 14A shows ESP maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective neutral states. Figure 14B shows ESP maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective semiquinone states. Figure 14C shows ESP maps of 2,3-dicyano-1,4-naphthoquinone (top) and 1,4-naphthoquinone (bottom) in their respective dianion states. In the ESP maps, darker shades indicate higher charge density (more electron-rich or electron-poor), and lighter shades indicate lower charge density (less electron-rich or electron-poor). As can be seen from Figures 14A-14C, the charge distribution is relatively similar between DCNQ and 1,4-naphthoquinone in the neutral (Figure 14A) and dianionic (Figure 14C) states. However, Figure 14B shows that the oxygen moiety of 1,4-naphthoquinone in its semiquinone state has significantly higher electron density than the oxygen moiety of DCNQ in its semiquinone state. The electron-withdrawing effect of the nitrile substituent is thought to withdraw electron density from the oxygen of DCNQ. Furthermore, this shift in electron density of DCNQ makes DCNQ thermodynamically and / or kinetically less reactive (e.g., pK) toward Lewis acids. a shifts the pK a All maps are at the same scale (imaged with van der Waals spheres).

[0136] 15A-15D show the calculated geometry and ESP maps of CO2 and SO2, respectively.

[0137] Example 4 This example describes the selective removal of a quantity of a first Lewis acid gas from a fluid mixture containing the first Lewis acid gas and a second, different Lewis acid gas by an electroactive species in its reduced state. In particular, a gas mixture containing SO2 and CO2 was exposed to the reduced form of DCNQ to remove SO2 to a greater extent than CO2 from the fluid mixture.

[0138] Gas separation experiments used a packed-bed bubble column apparatus containing a borosilicate glass tube (12" long, 0.23" internal diameter) filled with 8.6 g of 1 mm glass beads. The bubble column apparatus was oven-dried and sealed at each end with two septa. An inlet needle was inserted into the bottom of the column and an outlet needle was inserted into the top of the column. The column was flushed with dry nitrogen gas for 10 minutes to establish an inert atmosphere inside the column. All gas streams were applied to the column inlet at precise flow rates using Cole-Parmer mass flow controllers. The effluent stream of the bubble column apparatus was monitored for CO2 and SO2 gas concentrations. Figure 16 shows a schematic diagram of the gas separation experiments.

[0139] The doubly reduced DCNQ species, 2,3-dicyanonaphthoquinone dianion (DCNQ 2- ) was prepared by treating a solution of 2,3-dicyanonaphthoquinone (DCNQ) in tetrahydrofuran (THF) with sodium (Na) metal, filtering to remove residual metal, and evaporating to remove the THF. 2- The reaction scheme for preparing is shown below: [ka]

[0140] Prior to the gas trapping experiments, the column apparatus was loaded with 12 mM 2,3-dicyanonaphthoquinone dianion (DCNQ) in propylene carbonate. 2- The column was filled with 2.4 mL of DCNQ solution. The filling procedure was carried out under flowing nitrogen gas to maintain an inert atmosphere within the column. 2-After filling the column with the propylene carbonate solution, a dry nitrogen gas stream was introduced into the column inlet at a flow rate of 1 mL / min to equilibrate the system. The mass flow controller for the inlet gas was then connected to a SO2 / CO2 / N2 gas stream (1 mole percent (mol%) SO2, 10 mol% CO2, 89 mol% N2) at 1 mL / min, and data logging was immediately initiated. To control for the solvent physisorption of the Lewis acid gas, 2.4 mL of solvent (propylene carbonate) was used to elucidate the DCNQ 2- The same procedure was performed in the absence of

[0141] CO2 and SO2 concentrations were measured by physisorption and DCNQ. 2- For the chemisorption experiments, the total volume of inlet gas introduced into the system was measured. Due to the low solubility of CO2 in propylene carbonate, the physisorption experiments (i.e., DCNQ 2- It was observed that breakthrough in the chemisorption experiments (i.e., in the absence of DCNQ) occurred much earlier than that of SO2, which has a higher solubility in propylene carbonate. 2- It was observed that CO2 breakthrough occurred at a later time point in the chemisorption experiments than in the physisorption control experiments. 2- Approximately 70% stoichiometric capture of CO2 by the adduct DCNQ was demonstrated, as shown below. 2- DCNQ forming (CO2)2 2- This is thought to be due to the reversible reaction of CO2 with HCl. [ka]

[0142] However, DCNQ 2- CO2 complexed with the adduct DCNQ 2- It was replaced by SO2 in an irreversible reaction to form (SO2)2. 2-The (SO2)2 adduct formation was evident in the delayed breakthrough of SO2 in the chemisorption experiments compared to the breakthrough in the physisorption experiments. The difference in reactivity was observed qualitatively. After CO2 breakthrough, but before SO2 breakthrough, the entire solution in the column turned yellow (DCNQ 2- The color was pink (indicating the presence of (SO2)2), except for a small area near the column entrance that was observed to have a pink color (DCNQ 2- and DCNQ 2- At a later time point, after SO2 breakthrough, the entire column solution was observed to have a yellow color, indicating the absence of CO2 in the column and DCNQ throughout the column. 2- Figure 17A shows plots of the ratio of outlet gas concentration to inlet gas concentration versus time for the physisorption and chemisorption experiments. In Figure 17A, curve A corresponds to the CO concentration in the physisorption (propylene carbonate only) experiment, and curve B corresponds to the CO concentration in the chemisorption (DCNQ in propylene carbonate) experiment. 2- ) experiment, curve C corresponds to the CO2 concentration in the physisorption (propylene carbonate only) experiment, and curve D corresponds to the SO2 concentration in the chemisorption (DCNQ in propylene carbonate) experiment. 2- ) corresponds to the SO2 concentration in the experiment. The results in Figure 17A show significantly earlier breakthrough of CO2 than SO2, and also show that SO2 breakthrough is significantly delayed in the chemisorption experiment compared to the physisorption experiment. Figure 17B shows an expanded view of curves A and B from Figure 17A.

[0143] Delay in SO2 breakthrough is required for all departure DCNQ 2- This explains the stoichiometric reaction of SO2 with DCNQ 2- Reaction scheme for coupling to, and DCNQ 2- The replacement of CO2 by SO2 in the (CO2)2 adduct is shown below. [ka]

[0144] Gas separation experiment results demonstrated the selective capture of SO2 from a gas stream of 1% SO2, 10% CO2, and 89% N2. 2- Chemisorptive capture of SO2 by SO2 is considered to be only reversible via an oxidation reaction that releases SO2. Such oxidation can occur electrochemically or through the use of oxidizing chemical reagents.

[0145] While several embodiments of the present invention have been described and illustrated herein, those skilled in the art will readily envision various other means and / or structures for performing the functions and / or obtaining one or more of the results and / or advantages described herein, and each such variation and / or modification is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary, and that the actual parameters, dimensions, materials, and / or configurations will vary depending on the specific application or applications for which the teachings of the present invention are used. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein. Accordingly, it should be understood that the foregoing embodiments are presented by way of example only, and that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods is within the scope of the present invention, provided that such features, systems, articles, materials, and / or methods are not mutually inconsistent.

[0146] The indefinite articles "a" and "an," as used herein in the specification and claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0147] The phrase "and / or," as used herein in the specification and claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are present conjunctively in some cases and disjunctively in other cases. Unless clearly indicated to the contrary, other elements may optionally be present other than the elements specifically identified by the "and / or" clause, whether associated with specifically identified elements or not. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); and so forth.

[0148] As used herein and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" should be interpreted as being inclusive, i.e., including at least one of a number or list of elements, but also including more than one, and optionally including additional unlisted items. Terms clearly indicating the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," only refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or," as used herein, should be interpreted to indicate exclusive alternatives (i.e., "one or the other, but not both") only when preceded by exclusive terms such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0149] As used in this specification and claims, the phrase "at least one," referring to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows for elements, if desired, to be present other than those specifically identified in the list of elements to which the phrase "at least one" refers, whether related to the specifically identified elements or not. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently, "at least one of A and / or B") can refer to, in one embodiment, at least one A, optionally including more than one, with no B present (optionally including elements other than B); in another embodiment, at least one B, optionally including more than one, with no A present (optionally including elements other than A); in yet another embodiment, at least one A, optionally including more than one, and at least one B, optionally including other elements; etc.

[0150] In the claims and the foregoing specification, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," and the like, are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the U.S. Patent and Trademark Office Manual of Examining Procedures, Section 2111.03. The present invention provides, for example, the following items. (Item 1) a chamber configured to receive a fluid mixture, the chamber including a negative electrode in electronic communication with the electroactive species; 1. An electrochemical device comprising: In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas but in which reaction with a second Lewis acid gas comprising one or more species selected from carbon dioxide, nitric oxide, RB, or RS (each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl) is thermodynamically and / or kinetically unfavorable at at least one temperature; 1. An electrochemical device comprising: (Item 2) Item 10. The electrochemical device of item 1, wherein the electroactive species is present in a liquid within the electrochemical device. (Item 3) Item 10. The electrochemical device of item 1, wherein the electroactive species is immobilized on the negative electrode. (Item 4) 4. The electrochemical device of any one of items 1 to 3, wherein the electroactive species comprises one or more organic species selected from optionally substituted quinones, optionally substituted thiolates, optionally substituted bipyridines, optionally substituted phenazines, and optionally substituted phenothiazines. (Item 5) In the at least one reduced state, the electroactive species has a pK of the first Lewis acid gas. a or greater than the pK of carbon dioxide a pK is less than a 5. The electrochemical device according to any one of items 1 to 4, comprising a portion having: (Item 6) The first Lewis acid gas is sulfur dioxide (SO2), sulfur oxide (SO x ), nitric oxide (NO x6. The electrochemical device of any one of items 1 to 5, wherein the R is a gas selected from the group consisting of CI-C alkyl, aryl, cyclyl, heteroaryl, and heterocyclyl. (Item 7) 7. The electrochemical device according to any one of items 1 to 6, wherein R2S is hydrogen sulfide (H2S). (Item 8) 8. The electrochemical device according to any one of items 1 to 7, wherein R3B is borane. (Item 9) Item 9. The electrochemical device of item 8, wherein the borane is BH3. (Item 10) 7. The electrochemical device of any one of items 1 to 6, wherein the electroactive species has at least one reduced state in which it is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is thermodynamically unfavorable at at least one temperature. (Item 11) 11. The electrochemical device of any one of items 1 to 10, wherein the electroactive species has at least one reduced state in which it is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is kinetically unfavorable at at least one temperature. (Item 12) 12. The electrochemical device of any one of items 1 to 11, wherein the electroactive species has at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is thermodynamically unfavorable at at least one temperature of 223 K or greater. (Item 13) 13. The electrochemical device of any one of items 1 to 12, wherein the electroactive species has at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is kinetically unfavorable at at least one temperature of 223 K or greater. (Item 14) 14. The electrochemical device of any one of items 1 to 13, wherein the electroactive species has at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is thermodynamically unfavorable at at least one temperature of 223 K or greater and 573 K or less. (Item 15) 15. The electrochemical device of any one of items 1 to 14, wherein the electroactive species has at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is kinetically unfavorable at at least one temperature of 223 K or greater and 573 K or less. (Item 16) 16. The electrochemical device of any one of items 1 to 15, wherein the electroactive species has at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with carbon dioxide is thermodynamically unfavorable at at least one temperature of 223 K or greater and 373 K or less. (Item 17) The electroactive species is capable of combining with a first Lewis acid gas, but reacts with carbon dioxide at at least one temperature of 223 K or greater and 373 K or less. 17. The electrochemical device according to any one of items 1 to 16, wherein the electroactive species has at least one reduced state that is kinetically unfavorable in the presence of an electrochemical reaction. (Item 18) 18. The electrochemical device of any one of items 1 to 17, wherein the electroactive species has at least one reduced state in which the electroactive species can combine with a first Lewis acid gas, but reaction with carbon dioxide is thermodynamically unfavorable at 298 K. (Item 19) 19. The electrochemical device of any one of items 1 to 18, wherein the electroactive species has at least one reduced state in which the electroactive species can combine with a first Lewis acid gas, but reaction with carbon dioxide is kinetically unfavorable at 298 K. (Item 20) 20. The electrochemical device according to any one of items 1 to 19, wherein the negative electrode is part of an electrochemical cell comprising the negative electrode and a positive electrode. (Item 21) 21. The electrochemical device of claim 20, wherein the negative electrode comprises an electroactive composite layer comprising the electroactive species. (Item 22) 22. The electrochemical device according to any one of items 20 to 21, wherein the electroactive species is a first electroactive species and the positive electrode comprises a second electroactive species. (Item 23) Item 24: The electrochemical device according to any one of items 1 to 22, further comprising the conductive medium. 24. The electrochemical device according to any one of items 1 to 23, wherein the conductive medium comprises a non-volatile electrolyte. (Item 25) 25. The electrochemical device according to any one of items 1 to 24, wherein the conductive medium comprises a liquid. (Item 26) 26. The electrochemical device according to any one of items 1 to 25, wherein the conductive medium comprises an ionic liquid at room temperature. (Item 27) 27. The electrochemical device according to any one of items 1 to 26, wherein the electrochemical device comprises a plurality of the chambers fluidly connected in series. (Item 28) applying a potential difference across the electrochemical cell; exposing a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas to the electrochemical cell; removing a quantity of the first Lewis acid gas from the fluid mixture during and / or after applying the potential difference; and removing from the fluid mixture essentially none, or 10% or less by mole percent, of the second Lewis acid gas present in the fluid mixture. (Item 29) exposing a fluid mixture comprising a first Lewis acid gas and a second Lewis acid gas to one or more electroactive species in a reduced state; combining a quantity of the first Lewis acid gas with a first portion of the one or more electroactive species in a reduced state to form a first Lewis acid gas-electroactive species composite; combining an amount of the second Lewis acid gas with a second portion of the one or more electroactive species in a reduced state to form a second Lewis acid gas-electroactive species complex; and oxidizing at least a portion of the second Lewis acid gas-electroactive species complex so that an amount of the second Lewis acid gas is released from the second Lewis acid gas-electroactive species complex while essentially no first Lewis acid gas is released from the first Lewis acid gas-electroactive species complex, or an amount of the first Lewis acid gas that is 10% or less by mole percent of the amount of the first Lewis acid gas-electroactive species complex that is released from the first Lewis acid gas-electroactive species complex; A method comprising: (Item 30) The first Lewis acid gas is sulfur dioxide (SO2), sulfur oxide (SO x ), nitric oxide (NO x 29. The method of claim 28, wherein the gas is selected from the group consisting of methyl methyl ether (Methyl ether), ... (Item 31) 31. The method of any one of items 28-30, wherein the second Lewis acid gas comprises one or more species selected from carbon dioxide, nitric oxide, R3B, or R2S, and each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl. (Item 32) 32. The method according to any one of items 28 to 31, wherein the second Lewis acid gas is carbon dioxide (CO2). (Item 33) The method according to any one of Items 30 to 32, wherein R2S is hydrogen sulfide (H2S). (Item 34) 34. The method according to any one of items 30 to 33, wherein R3B is borane. (Item 35) 35. The method of claim 34, wherein the borane is BH3. (Item 36) 36. The method according to any one of items 28 to 35, wherein the fluid mixture is a gas mixture or a liquid mixture. (Item 37) 37. The method of any one of items 29 to 36, wherein the oxidizing step comprises exposing the second Lewis acid gas-electroactive species complex to an electrochemical cell while simultaneously applying a potential difference across the electrochemical cell. (Item 38) 38. The method of any one of items 29 to 37, wherein the oxidation step is a first oxidation step carried out for a first period of time, and the method further comprises a second oxidation step comprising oxidizing at least a portion of the first Lewis acid gas-electroactive species complex for a second period of time, such that an amount of the first Lewis acid gas is released from the first Lewis acid-electroactive species complex. (Item 39) 39. The method of claim 38, wherein the second oxidation step comprises exposing the second Lewis acid gas-electroactive species complex to the electrochemical cell while simultaneously applying a potential difference across the electrochemical cell. (Item 40) the first oxidation step comprising exposing the second Lewis acid gas-electroactive species complex to a first electrochemical cell while simultaneously applying a potential difference across the first electrochemical cell; The second oxidation step comprises converting the first Lewis acid gas-electroactive species complex into a second electroactive species complex. applying a potential difference across said second electrochemical cell while exposing said first electrochemical cell to said second electrochemical cell; Item 39. The method according to item 38. (Item 41) 41. The method according to any one of items 29 to 40, further comprising reducing the electroactive species in an oxidized state to form the electroactive species in a reduced state before the step of exposing the fluid mixture containing the first Lewis acid gas and the second Lewis acid gas to electroactive species. (Item 42) 42. The method of claim 41, wherein the reducing step comprises applying a potential difference across an electrochemical cell comprising a negative electrode in electronic communication with the electroactive species. (Item 43) 43. The method of any one of items 28 to 42, wherein the electrochemical cell comprises a negative electrode in electronic communication with the electroactive species. (Item 44) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is thermodynamically unfavorable at at least one temperature; 44. The method according to any one of Items 29 to 43, comprising: (Item 45) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is kinetically unfavorable at at least one temperature; 45. The method according to any one of Items 29 to 44, comprising: (Item 46) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is thermodynamically unfavorable at at least one temperature at or above 223 K; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 47) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is kinetically unfavorable at at least one temperature of 223 K or greater; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 48) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but reaction with the second Lewis acid is thermodynamically unfavorable at at least one temperature of 223 K or greater and 573 K or less; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 49) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is kinetically unfavorable at at least one temperature of 223 K or greater and 573 K or less; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 50) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is thermodynamically unfavorable at at least one temperature of 223 K or greater and 373 K or less; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 51) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas, but in which reaction with the second Lewis acid is kinetically unfavorable at at least one temperature of 223 K or greater and 373 K or less; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 52) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas but in which reaction with the second Lewis acid is thermodynamically unfavorable at 298 K; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 53) In at least one conductive medium, the electroactive species is in the oxidized state, and at least one reduced state in which the electroactive species is capable of combining with a first Lewis acid gas but in which reaction with the second Lewis acid is kinetically unfavorable at 298 K; 46. ​​The method according to any one of Items 29 to 45, comprising: (Item 54) 54. The method of any one of items 29 to 53, wherein the electroactive species comprises one or more organic species selected from optionally substituted quinones, optionally substituted thiolates, optionally substituted bipyridines, optionally substituted phenazines, and optionally substituted phenothiazines. (Item 55) the electroactive species having an oxidized state and at least one reduced state, wherein in the at least one reduced state, the electroactive species has a pK aor greater than the pK of the second Lewis acid gas a pK is less than a 55. The method according to any one of items 29 to 54, comprising a moiety having the formula: (Item 56) Item 56. The method of item 55, wherein the electrochemical cell comprises a negative electrode and a positive electrode. (Item 57) 57. The method of claim 56, wherein the negative electrode comprises an electroactive composite layer comprising the electroactive species. (Item 58) 58. The method according to any one of items 56 to 57, wherein the electroactive species is a first electroactive species and the positive electrode comprises a second electroactive species.

Claims

1. A step of exposing a fluid mixture comprising a first gas containing a first Lewis acid and a second gas containing a second Lewis acid to one or more electroactive species in a reduced state, wherein the first gas containing the first Lewis acid has a different chemical structure from the second gas containing the second Lewis acid. The steps of forming a first composite between a portion or all of the first Lewis acid from the first gas and a first portion of the one or more electroactive species in the reduced state, The steps of forming a second composite between some or all of the second Lewis acid from the second gas and the second portion of the one or more electroactive species in the reduced state, A step of oxidizing at least a portion of the second composite, wherein the first composite is not oxidized at all, or is oxidized to 70 mol% or less of the first composite. Methods that include...

2. The method according to claim 1, wherein the step of forming the first composite is carried out by bonding some or all of the first Lewis acid to the first portion of one or more electroactive species in the reduced state.

3. The method according to any one of claims 1 to 2, wherein the step of forming the second composite is carried out by bonding some or all of the second Lewis acid to the second portion of one or more electroactive species in the reduced state.

4. The method according to any one of claims 1 to 3, wherein the step of oxidizing at least a portion of the second composite comprises the step of dissociating at least a portion of the second composite and the step of releasing some or all of the second Lewis acid from the second composite.

5. The method according to any one of claims 1 to 4, wherein the step of oxidizing at least a portion of the second composite is carried out in such a way that the first composite is not oxidized at all, or is oxidized by 10 mol% or less of the first composite.

6. The method according to any one of claims 1 to 5, wherein the fluid mixture is a gas mixture or a liquid mixture.

7. The method according to any one of claims 1 to 6, wherein the exposure step is carried out in the presence of a liquid containing an electrolyte solution.

8. The method according to claim 7, wherein the liquid containing the electrolyte solution contains one or more electroactive species.

9. The method according to any one of claims 1 to 8, wherein the step of oxidizing at least a portion of the second composite comprises exposing the second composite to an oxidation potential generated by applying a potential difference across an electrochemical cell.

10. The method according to claim 9, wherein the step of oxidizing at least a portion of the second composite comprises exposing the second composite to the electrochemical cell.

11. The method according to any one of claims 1 to 9, wherein, at least during the step of exposing the fluid mixture to one or more electroactive species in a reduced state, the one or more electroactive species are dissolved in a liquid that is a phase separate from the fluid mixture.

12. The method according to any one of claims 1 to 10, wherein the step of oxidizing at least a portion of the second composite is carried out during a first period, and the method further includes the step of oxidizing at least a portion of the first composite as part of a second oxidizing step carried out during a second period.

13. The method according to claim 12, wherein the step of oxidizing at least a portion of the first composite comprises exposing the first composite to an oxidation potential generated by applying a potential difference across an electrochemical cell.

14. The step of oxidizing at least a portion of the second composite comprises exposing the second composite to an oxidation potential generated by applying a potential difference across a first electrochemical cell, The method according to claim 13, wherein the step of oxidizing at least a portion of the first composite comprises exposing the first composite to an oxidation potential generated by applying a potential difference across a second electrochemical cell.

15. The method according to claim 14, wherein the potential difference applied across the first electrochemical cell is different from the potential difference applied across the second electrochemical cell.

16. The method according to any one of claims 1 to 15, wherein the step of oxidizing at least a portion of the first composite comprises the step of dissociating at least a portion of the first composite, and the step of releasing some or all of the first Lewis acid gas from the first composite.

17. The method according to any one of claims 1 to 16, wherein the first Lewis acid is selected from sulfur dioxide (SO₂), sulfur oxide (SO₂x), nitrogen oxide (NO₂x), R₂S, carbonyl sulfide (COS), R₃B, boron trifluoride (BF₃), or a combination thereof, and each R is independently H, branched or unbranched C₁-C₸ alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl.

18. The method according to claim 17, wherein R₂S is hydrogen sulfide (H₂S).

19. The method according to any one of claims 1 to 18, wherein the second Lewis acid comprises one or more species selected from carbon dioxide, nitrogen oxide, R3B, or R2S, and each R is independently H, branched or unbranched C1-C8 alkyl, aryl, cyclyl, heteroaryl, or heterocyclyl.

20. The method according to any one of claims 1 to 19, wherein the second Lewis acid gas is carbon dioxide (CO₂).

21. The method according to any one of claims 1 to 20, wherein the one or more electroactive species comprises one or more organic species selected from substituted or unsubstituted quinones, substituted or unsubstituted thioates, substituted or unsubstituted bipyridines, substituted or unsubstituted phenazines, and substituted or unsubstituted phenothiazines.

22. The method according to any one of claims 1 to 21, wherein the oxidation step is carried out with an oxidizing agent having sufficient oxidizing power to oxidize the second composite but insufficient oxidizing power to oxidize the first composite under the conditions of the method.

23. The method according to any one of claims 1 to 21, wherein the affinity between the first gas and the electroactive species in its oxidized state is strong enough to maintain the composite between the first Lewis acid and the electroactive species under the conditions of the method and prevent the release of the first Lewis acid.

24. The method according to any one of claims 1 to 21, wherein the oxidation step is carried out electrochemically at an oxidation potential that is sufficient to oxidize the second composite but insufficient to oxidize the first composite under the conditions of the method.

25. The method according to any one of claims 1 to 21, further comprising the step of reducing the oxidized electroactive species to form the reduced electroactive species, prior to the step of exposing the fluid mixture comprising the first gas and the second gas to the electroactive species.

26. The method of claim 25, wherein the reducing step includes applying a potential difference across an electrochemical cell including a negative electrode in electronic communication with the electroactive species.

27. ​​The method according to claim 26, wherein the electroactive species is a first electroactive species, and the electrochemical cell including the negative electrode further includes a positive electrode including a second electroactive species.

28. The method according to claim 27, wherein the second electroactive species is of the same type as the first electroactive species.

29. The method according to claim 27, wherein the second electroactive species has the same composition as the first electroactive species.

30. The method according to any one of claims 25 to 29, wherein the electroactive species is dissolved or suspended in a liquid solution during the reducing step.

31. The method according to any one of claims 1 to 30, wherein at least a portion of the exposure step is carried out in an absorber column.

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